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Abstract:

An apparatus for identifying interconnections in a network. The apparatus
comprises a plurality of transmitter coupling units, a plurality of
receiver coupling units, and an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network. In
some embodiments, the interconnection identification means is configured
to, if any one of the transmitter coupling units is coupled to the same
cable line as a selected one of the receiver coupling units, identify the
interconnection between the transmitter coupling unit and the selected
receiver coupling unit according to by a binary tree search algorithm.

Claims:

1. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line; and
an interconnection identification means configured to identify
interconnections between the transmitter coupling units and the receiver
coupling units by cable lines in the network; wherein the interconnection
identification means is configured to, if any one of the transmitter
coupling units is coupled to the same cable line as a selected one of the
receiver coupling units, identify the interconnection between the
transmitter coupling unit and the selected receiver coupling unit by: (i)
selecting a subset of the transmitter coupling units; (ii) conveying, at
least once, the same test signal to each of the transmitter coupling
units in the selected subset at substantially the same time so that, for
each of the transmitter coupling units in the selected subset that is
coupled to a respective cable line, the transmitter coupling unit couples
the test signal into the respective cable line; (iii) determining whether
the selected subset of transmitter coupling units includes a transmitter
coupling unit that is coupled to the same cable line as the selected
receiver coupling unit based on whether the selected receiver unit
couples out, from the cable line to which it is coupled, a test signal
which has propagated directly to the receiver coupling unit from one of
the transmitter coupling units in the selected subset; and (iv) selecting
a new subset of the transmitter coupling units based on the determination
in step (iii), and performing steps (ii) and (iii) for the newly selected
transmitter coupling units; and (v) if necessary, repeating step (iv)
until the interconnection between the transmitter coupling unit and the
selected receiver coupling unit is identified.

2. An apparatus according to claim 1, wherein the interconnection
identification means may be configured to identify either an
interconnection between one of the transmitter coupling units and the
selected receiver coupling unit or the absence of such an interconnection
by: (i) selecting a subset of the transmitter coupling units; (ii)
conveying, at least once, the same test signal to each of the transmitter
coupling units in the selected subset at substantially the same time so
that, for each of the transmitter coupling units in the selected subset
that is coupled to a respective cable line, the transmitter coupling unit
couples the test signal into the respective cable line; (iii) determining
whether the selected subset of transmitter coupling units includes a
transmitter coupling unit that is coupled to the same cable line as the
selected receiver coupling unit based on whether the selected receiver
unit couples out, from the cable line to which it is coupled, a test
signal which has propagated directly to the receiver coupling unit from
one of the transmitter coupling units in the selected subset; and (iv)
selecting a new subset of the transmitter coupling units based on the
determination in step (iii), and performing steps (ii) and (iii) for the
newly selected transmitter coupling units; and (v) if necessary,
repeating step (iv) until an interconnection between one of the
transmitter coupling units and the selected receiver coupling unit or the
absence of such an interconnection is identified.

3. An apparatus according to claim 1 or 2, wherein the interconnection
identification means is further configured so that, if it is determined
in step (iii) that the selected subset of transmitter coupling units
includes a transmitter coupling unit that is coupled to the same cable
line as the selected receiver coupling unit, then step (iv) includes: (a)
disregarding any transmitter coupling units that are not selected for the
selecting of any new subsets of the transmitter coupling units; and (b)
selecting a subset of the previously selected transmitter coupling units
as the new subset of the transmitter coupling units.

4. An apparatus according to claim 3, wherein step (b) includes selecting
a subset which contains half or approximately/substantially half of the
previously selected transmitter coupling units as the new subset of the
transmitter coupling units.

5. An apparatus according to any one of the previous claims, wherein the
interconnection identification means is further configured so that, if it
is determined in step (iii) that the selected subset of transmitter
coupling units does not include a transmitter coupling unit that is
coupled to the same cable line as the selected receiver coupling unit,
then step (iv) includes: (a) disregarding any transmitter coupling units
that are selected for the selecting of any new subsets of the transmitter
coupling units; and (b) selecting all or a subset of the not selected and
not disregarded transmitter coupling units as the new subset of the
transmitter coupling units.

6. An apparatus according to claim 5, wherein step (b) includes selecting
a subset which contains half or approximately/substantially half of the
not selected and not previously disregarded transmitter coupling units.

7. An apparatus according to any one of the previous claims, wherein the
selecting of a new subset of the transmitter coupling unit in step (iv)
based on the determination in step (iii) is made according to a binary
tree search algorithm.

8. An apparatus according to any one of the previous claims, wherein the
interconnection identification means includes a signal processing unit
configured to, if any of the receiver coupling units couples out a test
signal, analyse one or more characteristics of the test signal to
determine, based on the one or more analysed characteristics, whether the
test signal has propagated directly to the receiver coupling unit from
one of the transmitter coupling units.

9. An apparatus according to any one of the previous claims, wherein the
signal processing unit is configured to analyse one or more
characteristics of the test signal to determine, based on the one or more
analysed characteristics, which of the following conditions is true: (i)
the test signal is a direct signal which has propagated directly from a
transmitter coupling unit to the receiver coupling unit via a single
cable line to which the first and second coupling unit are coupled; (ii)
the test signal is a crosstalk signal that has propagated indirectly from
a transmitter coupling unit to the receiver coupling unit via one or more
coupling paths between different cable lines to which the transmitter and
receiver coupling units are respectively coupled.

10. An apparatus according to claim 9, wherein in step (iii), the signal
processing unit is used to determine whether the selected receiver unit
couples out, from the cable line to which it is coupled, a test signal
which has propagated directly to the receiver coupling unit from one of
the transmitter coupling units in the selected subset.

11. An apparatus according to any one of the previous claims, wherein:
each transmitter coupling unit includes two pairs of electrodes for
coupling a voltage signal into a respective cable line by non-contact
coupling with twisted pairs in the cable line so that the voltage signal
propagates between two or more of the twisted pairs; and step (ii)
includes conveying the same signal to a first pair of electrodes in each
of the transmitter coupling units in the selected subset at a
substantially the same first time and then, subsequently, conveying the
same signal to a second pair of electrodes in each of the transmitter
coupling units in the selected subset at a substantially the same second
time.

12. An apparatus according to any one of the previous claims, wherein the
apparatus is additionally for determining the physical state of cable
lines in the network and includes a state determining means configured to
determine the physical state of cable lines in the network using the
transmitter coupling units and the receiver coupling units.

13. An apparatus according to any one of the previous claims, wherein the
interconnection identification means includes: at least one signal
generating unit configured to generate the test signal; and conveying
means configured to convey the test signal generated by the at least one
signal generating unit to the plurality of transmitter coupling units.

14. An apparatus according to claim 13, wherein the conveying means
includes at least one splitter unit configured to receive the test signal
via a single input signal path from the signal generating unit and to
output the test signal via a plurality of output signal paths.

15. An apparatus according to claim 14, wherein each output signal path
of the at least one splitter unit includes a respective switch operable
to control whether a test signal is outputted via the output signal path
and/or a balun.

16. An apparatus according to claim 14 or 15, wherein the conveying means
includes at least one further splitter unit configured to receive the
test signal via a single input signal path from the output signal path of
a splitter unit and to output the test signal via a plurality of output
signal paths.

17. An apparatus according to any one of claims 14 to 16, wherein one or
more of the splitter units and/or further splitter units includes a test
signal detector for detecting a test signal from the at least one signal
generating unit.

18. An apparatus according to any one of claims 14 to 17, wherein the
interconnection identification means is configured to identify
interconnections between the signal generating unit, the splitter units
and/or the further splitter units by generating test signals using the
signal generating unit and detecting the test signals using one or more
of the test signal detectors.

19. An apparatus according to any one of claims 13 to 18, wherein the
conveying means includes switching means operable to control which of the
plurality of transmitter coupling units receives the test signal from the
signal generating unit, wherein the switching means includes: a
respective switch located in each output signal path of at least one
splitter unit; and/or a respective switch located in each output signal
path of at least one further splitter units.

20. An apparatus according to any one of the previous claims, wherein the
interconnection identification means includes: a signal analysing unit
for analysing a test signal coupled out from a cable line by one of the
plurality of receiver coupling units; and conveying means configured to
convey a test signal coupled out from a cable line by one of the
plurality of receiver coupling units to the signal analysing unit.

21. An apparatus according to claim 20, wherein the conveying means
includes switching means operable to couple any one of the plurality of
receiver coupling units to the signal analysing unit via a signal path
which is common to all receiver coupling units.

22. An apparatus according to claim 20 or 21, wherein the switching means
includes a respective switch located between each receiver coupling unit
and the common signal path.

23. A method of identifying interconnections in a network comprising a
plurality of cable lines using an apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; and a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the method includes identifying an interconnection between one of
the transmitter coupling units and a selected receiver coupling unit by:
(i) selecting a subset of the transmitter coupling units; (ii) conveying,
at least once, the same test signal to each of the transmitter coupling
units in the selected subset at substantially the same time so that, for
each of the transmitter coupling units in the selected subset that is
coupled to a respective cable line, the transmitter coupling unit couples
the test signal into the respective cable line; (iii) determining whether
the selected subset of transmitter coupling units includes a transmitter
coupling unit that is coupled to the same cable line as the selected
receiver coupling unit based on whether the selected receiver unit
couples out, from the cable line to which it is coupled, a test signal
which has propagated directly to the receiver coupling unit from one of
the transmitter coupling units in the selected subset; and (iv) selecting
a new subset of the transmitter coupling units based on the determination
in step (iii), and performing steps (ii) and (iii) for the newly selected
transmitter coupling units; and (v) if necessary, repeating step (iv)
until the interconnection between the transmitter coupling unit and the
selected receiver coupling unit is identified.

24. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means includes: at least
one signal generating unit configured to generate the test signal; and
conveying means configured to convey the test signal generated by the at
least one signal generating unit to the plurality of transmitter coupling
units; wherein the conveying means includes at least one splitter unit
configured to receive the test signal via a single input signal path from
the signal generating unit and to output the test signal via a plurality
of output signal paths.

25. An apparatus for identifying interconnections according to claim 24,
wherein the conveying means is as set out in any one of claims 13 to 19.

26. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means includes: at least
one signal generating unit configured to generate the test signal; and
conveying means configured to convey the test signal generated by the at
least one signal generating unit to the plurality of transmitter coupling
units; wherein the conveying means includes: at least one splitter unit
configured to receive the test signal via a single input signal path from
the signal generating unit and to output the test signal via a plurality
of output signal paths; optionally, at least one further splitter unit
configured to receive the test signal via a single input signal path from
the output signal path of a splitter unit and to output the test signal
via a plurality of output signal paths; wherein one or more of the
splitter units and/or further splitter units includes a test signal
detector for detecting a test signal from the at least one signal
generating unit.

27. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means includes: a signal
analysing unit for analysing a test signal coupled out from a cable line
by one of the plurality of receiver coupling units; and conveying means
configured to convey a test signal coupled out from a cable line by one
of the plurality of receiver coupling units to the signal analysing unit;
wherein the conveying means includes switching means operable to couple
any one of the plurality of receiver coupling units to the signal
analysing unit via a signal path which is common to all receiver coupling
units.

28. An apparatus for identifying interconnections according to claim 27,
wherein the conveying means is as set out in claim 21 or 22.

29. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means includes: at least
one signal generating unit configured to generate the test signal; and a
wander lead for coupling, via an additional transmitter coupling unit,
the test signal generated by the at least one signal generating unit into
any one of the cable lines in a network comprising a plurality of cable
lines.

30. An apparatus according to claim 29, wherein the wander lead includes
or is coupled to the additional transmitter coupling unit.

31. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means includes at least one
signal generating and/or analysing unit configured to generate the test
signal and/or analyse a test signal coupled out by one of the plurality
of receiver coupling units; wherein the at least one signal generating
and/or analysing unit includes a synch block which allows the signal
generating and/or analysing unit to be synchronised with other signal
generating and/or analysing units.

32. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means includes at least one
cable including a plurality of twisted pairs, wherein the interconnection
identification means is configured such that: a first twisted pair in the
at least one cable carries a test signal generated by a signal generating
unit; and/or a second twisted pair in the cable carries a first
communications signal for providing information from one component in the
interconnection identification means and/or state determining means to
another component in the interconnection identification means and/or
state determining means; and/or a third twisted pair in the cable carries
a second communications signal for providing information from one
component in the interconnection identification means and/or state
determining means to another component in the interconnection
identification means and/or state determining means, wherein the second
communications signal propagates in a direction opposite to that of the
first communications signal; and/or a fourth twisted pair in the cable
carriers power for powering one or more components of the interconnection
identification means.

33. An apparatus according to claim 32, wherein the interconnection
identification means and/or state determining means includes a signal
generating unit configured to generate the test signal.

34. An apparatus for identifying interconnections in a network comprising
a plurality of cable lines and/or for determining the physical state of
cable lines in the network, the apparatus having: a plurality of
transmitter coupling units, each transmitter coupling unit being
configured to couple to a respective cable line in a network comprising a
plurality of cable lines and to couple a test signal into the respective
cable line; a plurality of receiver coupling units, each receiver
coupling unit being configured to couple to a respective cable line in
the network and, if a test signal is present in the respective cable
line, to couple the test signal out from the respective cable line;
wherein the apparatus includes an interconnection identification means
configured to identify interconnections between the transmitter coupling
units and the receiver coupling units by cable lines in the network
and/or a state determining means configured to determine the physical
state of cable lines in the network using the transmitter coupling units
and the receiver coupling units; wherein the interconnection
identification means and/or state determining means is configured to
perform an installation sequence in which each transmitter coupling unit
and each receiver coupling unit is associated with a respective port in
the network.

35. An apparatus according to claim 34, wherein the interconnection
identification means is further configured to record in a database the
association of each transmitter coupling unit and each receiver coupling
unit with a respective port in the network.

36. An apparatus according to claim 34 or 35, wherein the installation
sequence comprises: (i) supplying prompts to a user; (ii) manual
inputting of data by the user in response to the prompts.

37. An apparatus according to any one of the previous claims, wherein:
each transmitter coupling unit is configured to couple a test signal into
a respective cable line in the network such that the test signal
propagates along the respective cable line between at least two twisted
pairs in the respective cable line; and/or each receiver coupling unit is
configured to couple a test signal out from a respective cable line in
the network after it has propagated between at least two twisted pairs in
the respective cable line.

38. An apparatus according to any one of the previous claims, wherein:
each transmitter coupling unit is configured to couple a test signal into
a respective cable line in the network by non-contact coupling with
conductors in the respective cable line; and/or each receiver coupling
unit is configured to couple a test signal out from a respective cable
line in the network by non-contact coupling with the conductors in the
respective cable line.

39. An apparatus according to any one of the previous claims, wherein the
or each test signal is a signal having characteristics such that, when it
is coupled out from a cable line by a receiver coupling unit, the
characteristics of the test signal can be analysed to determine whether
the resulting second test signal has propagated directly to the receiver
coupling unit from a transmitter coupling units.

40. An apparatus according to claim 39, wherein the or each test signal
is a signal suitable for performing time domain reflectometry and/or
frequency domain reflectometry.

41. An apparatus according to any one of the previous claims, wherein a
state determining means is configured to determine the physical state of
a cable line in the network by coupling a test signal into a selected
cable line using one of the transmitter coupling units, coupling a test
signal out of the selected cable line using one of the receiver coupling
units and analysing the test signal coupled out of the selected cable
line by the receiver coupling unit so as to determine a physical state of
the cable.

42. A kit of parts for forming an apparatus as set out in any one of the
previous claims.

43. A coupling unit for coupling a voltage signal to and/or from a cable
including a plurality of twisted pairs, the coupling unit having: a first
electrode and a second electrode arranged to produce an electric field
therebetween to couple a voltage signal to the cable by non-contact
coupling with the twisted pairs so that the voltage signal propagates
along the cable between at least two of the twisted pairs and/or arranged
to receive a voltage signal which has propagated along the cable between
at least two of the twisted pairs by non-contact coupling with at least
two of the twisted pairs between which the voltage signal has propagated;
wherein the first and/or second electrodes of the coupling unit are
located (preferably printed) on a flexible circuit board.

44. A coupling unit according to claim 43, wherein the first and/or
second electrodes of the coupling unit are printed on a flexible circuit
board.

45. A coupling unit according to claim 43 or 44, wherein the first and
second electrodes are located on one side of the flexible circuit board
and a ground plane is located on an opposite side of the flexible circuit
board to the first and second electrodes.

46. A coupling unit according to any one of claims 43 to 45, wherein the
flexible circuit board has a comb shape, with a plurality of projections
forming the comb shape and the first and second electrodes of the
coupling unit being located on a projection of the comb shape.

47. A coupling unit according to claim 46, wherein the coupling unit has
a third electrode and a fourth electrode arranged to produce an electric
field therebetween to couple a voltage signal to the cable by non-contact
coupling with the twisted pairs so that the voltage signal propagates
along the cable between at least two of the twisted pairs and/or arranged
to receive a voltage signal which has propagated along the cable between
at least two of the twisted pairs by non-contact coupling with at least
two of the twisted pairs between which the voltage signal has propagated,
wherein the third and fourth electrodes are located on a projection of
the comb shape that is different to that on which the first and second
electrodes of the coupling unit are mounted.

48. A coupling unit according to any one of claims 43 to 47, wherein the
coupling unit includes a clip made of resilient/elastic material, the
clip being configured to press the first and second electrodes, and
optionally third and fourth electrodes, of the coupling unit against the
sleeve of a twisted pair cable.

49. A coupling unit according to any one of claims 43 to 48, wherein the
flexible circuit board includes conductive pads for connecting the first
and second electrodes, and optionally third and fourth electrodes, to
corresponding pads on an external circuit board.

50. A coupling unit according to claim 49, wherein the flexible circuit
board is configured to be connected to the external circuit board by
clamping the conductive pads of the flexible circuit board against the
corresponding pads of the external circuit board.

51. An apparatus substantially as any one embodiment herein described
with reference to and as shown in the accompanying drawings.

52. A method substantially as any one embodiment herein described with
reference to and as shown in the accompanying drawings.

Description:

[0001] This invention relates to developments concerning apparatuses for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state (i.e. condition) of cable
lines in the network. In some embodiments, this invention may relate to
developments concerning apparatuses for both identifying interconnections
in a network comprising a plurality of cable lines and for determining
the physical state of cable lines in the network. The network may be a
local area network, for example.

[0002] In some embodiments, test signals are transmitted and received for
network inspection purposes. In some embodiments, the test signals are
coupled into out from the cable lines of the network using non-contacting
coupling units. Analysis of test signals coupled out from the cable lines
can used to identify interconnections in the network, e.g. so as to allow
a connection map of patch leads to be produced. Analysis of the test
signals can also be used be used to determine the physical state (i.e.
condition) of cable lines in the network, e.g. so as to ensure that
network data traffic can propagate correctly.

[0003] Cables which include a plurality of twisted pairs, referred to as
"twisted pair cables" herein, are well known. Such cables are commonly
used for telecommunications purposes, e.g. computer networking and
telephone systems. In the field of telecommunications, twisted pair
cables are usually provided without shielding, as unshielded twisted pair
(UTP) cables. However, shielded twisted pair (STP) cables are also known.

[0004] In this context, a "twisted pair" is a pair of conductors, usually
a forward conductor and a return conductor of a single circuit, which
have been twisted together. The conductors are usually twisted together
for the purposes of cancelling out electromagnetic interference from
external sources and to minimise crosstalk between neighbouring twisted
pairs within a cable comprising a plurality of twisted pairs. In this
way, each twisted pair provides a reliable respective communication
channel for a signal, usually a differential voltage signal, to be
conveyed within the twisted pair. Common forms of unshielded twisted pair
(UTP) cables are category 5 and category 6 UTP cables which include eight
conductors twisted together in pairs to form four twisted pairs.

[0005] The design and construction of twisted pair cables is carefully
controlled by manufacturers to reduce noise due to electromagnetic
interference and to reduce crosstalk between the twisted pairs within the
cables. To this end, each twisted pair in a twisted pair cable normally
has a different twist rate (i.e. number of twists per unit length along
the cable) from that of the other twisted pairs in the twisted pair
cable. It is also usual for the twisted pairs to be twisted around each
other within the cable. Fillets or spacers may be used to separate
physically the twisted pairs.

[0006] Networks including ports interconnected by a plurality of cables,
such as local area networks (LANs), are also well known. LANs are
typically used to enable equipment such as computers, telephones,
printers and the like to communicate with each other and with remote
locations via an external service provider. LANs typically utilise
twisted pair network cables, usually in the form of UTP cables.

[0007] The cables used in LANs are typically connected to dedicated
service ports throughout one or more buildings. The cables from the
dedicated service ports can extend through the walls, floor and/or
ceilings of the building to a communications hub, typically a
communications room containing a number of network cabinets. The cables
from wall and floor sockets within the building and from an external
service provider are also usually terminated within the communications
room.

[0008] A "patch system" may be used to interconnect various ports of the
LAN within the network cabinets. In a patch system, all cable lines in
the LAN can be terminated within the network cabinets in an organized
manner. The terminations of the cable lines in the network are provided
by the structure of the network cabinets, which are typically organised
in a rack system. The racks contain "patch panels", which themselves
utilise sets of ports, typically RJ-45 type connector ports, at which the
cable lines terminate.

[0009] Each of the ports in each patch panel is hard wired to one of the
cable lines in the LAN. Accordingly, each cable line is terminated on a
patch panel in an organized manner. In small patch systems, all cable
lines in the LAN may terminate on the patch panels of the same rack. In
larger patch systems, multiple racks are used, wherein different cable
lines terminate on different racks.

[0010] Interconnections between the various ports in the LAN are typically
made using "patch cables", which are usually UTP cables including four
twisted pairs. Each end of a patch cable is terminated by a connector,
such as an RJ-45 type connector for inserting into an RJ-45 type
connector port. One end of each patch cable is connected to the port of a
first cable line and the opposite end of the patch cable is connected to
the port of a second cable line. By selectively connecting the various
cable lines using the patch cables, a desired combination of network
interconnections can be achieved.

[0011] FIG. 1 shows a typical patch system organised into a server row, a
cross-connect row and a network row, which include patch panels. Patch
cables are used to interconnect two ports through the patch system.

[0012] In many businesses, employees of a company are assigned their own
computer network access number so that the employee can interface with
the company's IT infrastructure. When an employee changes office
locations, it is not desirable to provide that employee with newly
addressed port in the network. Rather, to preserve consistency in
communications, it is preferred that the exchanges of the ports in the
employee's old office be transferred to the telecommunications ports in
the employee's new location. This type of move is relatively frequent.
Similarly, when new employees arrive and existing employees depart, it is
usually necessary for the patch cables in the network cabinet(s) to be
rearranged so that each employee's exchanges can be received in the
correct location.

[0013] As the location of employees change, the patch cables in a typical
cabinet are often manually entered in a computer based log. This is
burdensome. Further, technicians often neglect to update the log each and
every time a change is made. Accordingly, the log is often less than 100%
accurate and a technician has no way of reading where each of the patch
cables begins and ends. Accordingly, each time a technician needs to
change a patch cable, that technician manually traces that patch cable
between an internal line and an external line. To perform a manual trace,
the technician locates one end of a patch cable. The technician then
manually follows the patch cable until he/she finds the opposite end of
that patch cable. Once the two ends of the patch cable are located, the
patch cable can be positively identified.

[0014] It takes a significant amount of time for a technician to manually
trace a particular patch cable, especially in large patch systems.
Furthermore, manual tracing is not completely accurate and a technician
may accidently go from one patch cable to another during a manual trace.
Such errors result in misconnected patch cables which must be later
identified and corrected.

[0015] Attempts have been made in the prior art to provide an apparatus
which can automatically trace the common ends of each patch cable within
local area networks, thereby reducing the labour and inaccuracy of manual
tracing procedures.

[0016] For example, U.S. Pat. No. 5,483,467 describes a patching panel
scanner for automatically providing an indication of the connection
pattern of the data ports within a LAN, so as to avoid the manual task of
identifying and collecting cable connection information. In one
embodiment, which is intended for use with shielded twisted pair cables,
the scanner uses inductive couplers which are associated with the data
ports. The inductive coupler is disclosed as being operative to impose a
signal on the shielding of shielded network cables in order to provide an
indication of the connection pattern produced by connection of the cables
to a plurality of ports.

[0017] In another embodiment of U.S. Pat. No. 5,483,467, the scanner is
coupled to each data port by "dry contact" with a dedicated conductor in
a patch cable. This is difficult to implement in practice, because most
network cables have to meet a particular pre-determined standard in the
industry, such as the RJ-45 type standard, in which there is no free
conductor which could be used for determining interconnectivity.

[0018] U.S. Pat. No. 6,222,908 discloses a patch cable identification and
tracing system in which the connectors of each patch cable contain a
unique identifier which can be identified by a sensor in the connector
ports of a telecommunications closet. By reading the unique identifier on
the connectors of each patch cable, the system can keep track of which
patch chords are being added to and removed from the system. Although
this system avoids the use of dedicated conductors in the patch cable, it
is difficult to implement because it requires use of non-standard patch
cables, i.e. patch cables with connectors containing unique identifiers.

[0019] International Patent Application Publication Number WO00/60475
discloses a system for monitoring connection patterns of data ports. This
system uses a dedicated conductor which is attached to the external
surface of a network cable in order to monitor the connection pattern of
data ports. Although this allows the system to be used with standard
network cables, it still requires the attaching of dedicated conductors
to the external surfaces of network cables and adapter jackets which are
placed over the standard network cable.

[0020] U.S. Pat. No. 6,285,293 discloses another system and method for
addressing and tracing patch cables in a dedicated telecommunications
system. The system includes a plurality of tracing interface modules that
attach to patch panels in a telecommunications closet. On the patch
panels, are located a plurality of connector ports that receive the
terminated ends of patch cables. The tracing interface modules mount to
the patch panels and have a sensor to each connector port which detects
whenever a patch cable is connected to the connector port. A computer
controller is connected to the sensors and monitors and logs all changes
to the patch cable interconnections in an automated fashion. However,
this system cannot be retrofitted to an existing network and relies on
the operator to work in a particular order if the patch cable connections
are to be accurately monitored.

[0021] International Patent Application Publication Number WO2005/109015,
which relates to the field of cable state testing, discloses a method of
determining the state of a cable comprising at least one electrical
conductor and applying a generated test signal to at least one conductor
of the cable by a non-electrical coupling transmitter. The reflected
signal is then picked up and compared with expected state signal values
for the cable, so that the state of the cable can be determined. The
present inventors have found that signals coupled to a twisted pair cable
by the methods described in WO2005/109015 have a tendency to leak out
from the twisted pair cable, especially when other twisted pair cables
are nearby.

[0022] GB2468925, US2011/0181374 and WO2010/109211, by the present
inventors, and the content of which is herewith incorporated in its
entirety, each describe apparatuses and methods for coupling a signal to
and from a twisted pair cable by non-contact coupling with twisted pairs
in the twisted pair cable, such that the signal propagates along the
cable between at least two of the twisted pairs. Such signals may be used
to determine interconnections, e.g. within a local area network. These
patent applications generally relates to a discovery that a twisted pair
cable, e.g. an unshielded twisted pair (UTP) cable, provides
communication channels which are additional to the respective
communication channel provided within each twisted pair in the cable. In
particular, it has been found that additional communication channels
exist between each combination of two twisted pairs within a twisted pair
cable, due to coupling between the twisted pairs. Each combination of two
twisted pairs within a twisted pair cable has been termed a
"pair-to-pair" combination. Therefore, the additional communication
channels may be termed "pair-to-pair" channels. GB2468925 discloses that
a signal which propagates along a twisted pair cable between two of the
twisted pairs can propagate reliably and over useful distances, without
significantly altering the transmission of signals within the individual
twisted pairs. Consequently, the "pair-to-pair" signal can propagate in
addition to the differential voltage signals which typically propagate
within each twisted pair when the twisted pair cable is in use. Therefore
the test signals can be introduced into the "pair-to-pair" channel and
these the "pair-to-pair" signals can be used to monitor the operation of
the network without disrupting the normal operation of the network.

[0023] UK patent application GB1009184.1, also by the present inventors,
and the content of which is herewith incorporated in its entirety,
discloses signal processing apparatuses and methods for use with a
plurality of cable lines, e.g. cable lines including one or more twisted
pair cables. In particular, GB1009184.1 relates to apparatuses and
methods for analysing one or more characteristics of a test signal
coupled out from one of a plurality of cable lines. GB1009184.1 patent
application presents apparatuses and methods for analysing a
characteristic of a test signal, e.g. a "pair-to-pair" signal, coupled
out by a coupling unit, to determine whether that test signal has
propagated directly to the coupling unit via a single cable line or has
propagated indirectly to the coupling unit via crosstalk between
different cable lines. A copy of UK patent application number GB1009184.1
is annexed to this patent application.

[0024] The present invention has been devised in light of the above
considerations.

[0025] In general, the present invention relates to developments
concerning an apparatus for identifying interconnections in a network
comprising a plurality of cable lines and/or for determining the physical
state of cable lines in the network, the apparatus having:

[0026] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line; and

[0027] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0028] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units.

[0029] As described below in further detail, such an apparatus may use
non-contact coupling units as disclosed in GB2468925 and/or a signal
processing unit as disclosed in UK patent application GB1009184.1, a copy
of which is annexed hereto. The apparatus may operate in parallel with
the network. The following disclosure relates to, amongst other things,
an example of the hardware functionality required to realise such an
apparatus; an installation sequence for the apparatus such that the
apparatus can be easily fitted onto the network; and the functionality
underpinning the apparatus, which may be implemented in software.

[0030] For the avoidance of any doubt, if the apparatus is for both
identifying interconnections in a network comprising a plurality of cable
lines and for determining the physical state of cable lines in the
network, the interconnection identification means may use the same
hardware as the state determining means.

[0031] In a first aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines, the apparatus having:

[0032] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0033] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line; and

[0034] an interconnection identification means configured to identify
interconnections between the transmitter coupling units and the receiver
coupling units by cable lines in the network;

[0035] wherein the interconnection identification means is configured to,
if any one of the transmitter coupling units is coupled to the same cable
line as a selected one of the receiver coupling units, identify the
interconnection between the transmitter coupling unit and the selected
receiver coupling unit by:

[0036] (i) selecting a subset of the transmitter coupling units;

[0037] (ii) conveying, at least once, the same test signal to each of the
transmitter coupling units in the selected subset at substantially the
same time so that, for each of the transmitter coupling units in the
selected subset that is coupled to a respective cable line, the
transmitter coupling unit couples the test signal into the respective
cable line;

[0038] (iii) determining whether the selected subset of transmitter
coupling units includes a transmitter coupling unit that is coupled to
the same cable line as the selected receiver coupling unit based on
whether the selected receiver unit couples out, from the cable line to
which it is coupled, a test signal which has propagated directly to the
receiver coupling unit from one of the transmitter coupling units in the
selected subset; and

[0039] (iv) selecting a new subset of the transmitter coupling units based
on the determination in step (iii), and performing steps (ii) and (iii)
for the newly selected transmitter coupling units; and

[0040] (v) if necessary, repeating step (iv) until the interconnection
between the transmitter coupling unit and the selected receiver coupling
unit is identified.

[0041] Identifying an interconnection in this way has been found to be
much more efficient in quickly identifying an interconnection between
transmitter and receiver coupling units than other methodologies, e.g. in
which a test signal is coupled to the transmitter coupling units one at a
time.

[0042] In this context, a signal which has propagated directly from one
coupling unit to another is a signal which propagates along a cable line
to which both coupling units are coupled, i.e. in contrast to a signal
which propagates indirectly from one coupling unit to another e.g. via
one or more coupling paths between different cable lines to which the
coupling units are respectively coupled.

[0043] For the avoidance of doubt, the same test signal may be conveyed to
each of the transmitter coupling units in a selected subset at
substantially the same time in many different ways, e.g. by generating a
test signal in a single signal generating unit and splitting the test
signal so it can be conveyed to more than one transmitter coupling unit
e.g. using one or more splitter unit as described below, and/or by
generating the same test signal independently using a plurality of signal
generating units so that the same test signal can be conveyed to more
than one transmitter coupling unit e.g. using one or more splitter unit
as described below.

[0044] Preferably, the interconnection identification means is also
configured to identify the absence of an interconnection between the
selected receiver coupling unit and any of the transmitter coupling
units. Thus, the interconnection identification means may be configured
to identify either an interconnection between one of the transmitter
coupling units and the selected receiver coupling unit or the absence of
such an interconnection, depending on which of these conditions is true.

[0045] Accordingly, the interconnection identification means may be
configured to identify either an interconnection between one of the
transmitter coupling units and the selected receiver coupling unit or the
absence of such an interconnection by:

[0046] (i) selecting a subset of the transmitter coupling units;

[0047] (ii) conveying, at least once, the same test signal to each of the
transmitter coupling units in the selected subset at substantially the
same time so that, for each of the transmitter coupling units in the
selected subset that is coupled to a respective cable line, the
transmitter coupling unit couples the test signal into the respective
cable line;

[0048] (iii) determining whether the selected subset of transmitter
coupling units includes a transmitter coupling unit that is coupled to
the same cable line as the selected receiver coupling unit based on
whether the selected receiver unit couples out, from the cable line to
which it is coupled, a test signal which has propagated directly to the
receiver coupling unit from one of the transmitter coupling units in the
selected subset; and

[0049] (iv) selecting a new subset of the transmitter coupling units based
on the determination in step (iii), and performing steps (ii) and (iii)
for the newly selected transmitter coupling units; and

[0050] (v) if necessary, repeating step (iv) until an interconnection
between one of the transmitter coupling units and the selected receiver
coupling unit or the absence of such an interconnection is identified.

[0051] The selecting of a new subset of the transmitter coupling unit in
step (iv) based on the determination in step (iii) may be made according
to a large number of possible search algorithms.

[0052] For example, the interconnection identification means may be
further configured so that, if it is determined in step (iii) that the
selected subset of transmitter coupling units includes a transmitter
coupling unit that is coupled to the same cable line as the selected
receiver coupling unit, then step (iv) includes:

[0053] (a) disregarding any transmitter coupling units that are not
selected for the selecting of any new subsets of the transmitter coupling
units; and

[0054] (b) selecting a subset of the previously selected transmitter
coupling units as the new subset of the transmitter coupling units.

[0055] Preferably, step (b) includes selecting a subset which contains
half or approximately/substantially half of the previously selected
transmitter coupling units as the new subset of the transmitter coupling
units. This has been found to be found a particularly efficient way to
identify an interconnection, and may form part of a binary tree search
algorithm, e.g. as described below.

[0056] Preferably, the interconnection identification means is further
configured so that, if it is determined in step (iii) that the selected
subset of transmitter coupling units does not include a transmitter
coupling unit that is coupled to the same cable line as the selected
receiver coupling unit, then step (iv) includes:

[0057] (a) disregarding any transmitter coupling units that are selected
for the selecting of any new subsets of the transmitter coupling units;
and

[0058] (b) selecting all or a subset of the not selected and not
disregarded transmitter coupling units as the new subset of the
transmitter coupling units.

[0059] Preferably, step (b) includes selecting a subset which contains
half or approximately/substantially half of the not selected and not
(previously) disregarded transmitter coupling units. This has been found
to be found a particularly efficient way to identify an interconnection,
and may form part of a binary tree search algorithm, e.g. as described
below.

[0060] The selecting of a new subset of the transmitter coupling unit in
step (iv) based on the determination in step (iii) may be made according
to a binary tree search algorithm. The binary tree search algorithm may
involve, for example, initially selecting a subset preferably containing
half or approximately/substantially half of the selected transmitter
coupling units in step (i). If, in step (iii) it is determined that the
selected subset does not include a transmitter coupling unit that is
coupled to the same cable line as the selected receiver unit, then a
subset containing the remaining transmitter units is selected as a new
subset in step (iv). If, it is then determined that this subsequently
selected subset does not include a transmitter coupling unit, then the
absence of an interconnection between the selected receiver coupling unit
and any of the transmitter coupling units can be identified. However, if
it determined for either selected subset that the selected subset
includes a transmitter coupling unit that is coupled to the same cable
line as the selected receiver unit, then a subset preferably containing
half or approximately/substantially half of the previously selected
transmitter coupling units is then selected as a new subset. This can be
repeated until the interconnection between one of the transmitter
coupling units and the selected receiver coupling unit is identified.

[0061] In some embodiments, the determination in step (iii) of whether the
selected receiver unit couples out, from the cable line to which it is
coupled, a test signal which has propagated directly to the receiver
coupling unit from one of the transmitter coupling units in the selected
subset, may be a trivial task if there is little or no crosstalk between
cable lines in the network.

[0062] However, the presence of crosstalk between cable lines in the
network may make it more difficult to determine whether the selected
receiver unit couples out, from the cable line to which it is coupled, a
test signal which has propagated directly to the receiver coupling unit
from one of the transmitter coupling units in the selected subset.
Crosstalk has been found to create particular difficulties for
determining whether a signal which has propagated between at least two
conductors in a cable, e.g. a signal which has propagated between two
twisted pairs in a cable, has propagated directly to the receiver
coupling unit from one of the transmitter coupling units in the selected
subset or has propagated indirectly, e.g. via one or more coupling paths
between different cable lines. However, such difficulties can be overcome
using the techniques described in UK patent application number 1009184.1,
a copy of which is annexed hereto. In particular, this UK patent
application describes how to determine whether a signal which has
propagated between at least two conductors in a cable line has propagated
directly from a transmitter ("first") coupling unit to a receiver
("second") coupling unit, by analysing one or more characteristics of the
signal coupled out from a cable line by the receiver coupling unit.

[0063] Accordingly, the interconnection identification means may include a
signal processing unit configured to, if any of the receiver coupling
units couples out a test signal, analyse one or more characteristics of
the test signal to determine, based on the one or more analysed
characteristics, whether the test signal has propagated directly to the
receiver coupling unit from one of the transmitter coupling units. The
signal processing unit may be configured to analyse one or more
characteristics of the test signal to determine, based on the one or more
analysed characteristics, which of the following conditions is true: (i)
the test signal is a direct signal which has propagated directly from a
transmitter coupling unit to the receiver coupling unit via a single
cable line to which the first and second coupling unit are coupled; (ii)
the test signal is a crosstalk signal that has propagated indirectly from
a transmitter coupling unit to the receiver coupling unit via one or more
coupling paths between different cable lines to which the transmitter and
receiver coupling units are respectively coupled.

[0064] Thus, in step (iii), the signal processing unit may be used to
determine whether the selected receiver unit couples out, from the cable
line to which it is coupled, a test signal which has propagated directly
to the receiver coupling unit from one of the transmitter coupling units
in the selected subset. The signal processing unit may be form part of a
signal analysing unit included in the interconnection identification
means.

[0065] The interconnection identification means may be configured so that
step (ii) includes conveying, more than once, the same test signal to
each of the transmitter coupling units in the selected subset at
substantially the same time. Conveying the same test signal to each of
the transmitter coupling units in the selected subset twice or more than
twice may be useful, for example, in embodiments in which each
transmitter coupling unit includes two pairs of electrodes for coupling a
voltage signal into a respective cable line by non-contact coupling with
twisted pairs in the cable line so that the voltage signal propagates
between two or more of the twisted pairs. Having two separate pairs of
electrodes for coupling a voltage signal into a twisted pair cable was
disclosed, for example, in GB2468925, US2011/0181374 and WO2010/109211,
and it is useful to avoid the problem of one of the pairs of electrodes
in a transmitter coupling unit being in a "null" location such that the
signal it couples into a twisted pair cable is not received by a receiver
coupling unit. Accordingly, step (ii) may in some embodiments include
conveying the same signal to a first pair of electrodes in each of the
transmitter coupling units in the selected subset at a substantially the
same first time and then, subsequently, conveying the same signal to a
second pair of electrodes in each of the transmitter coupling units in
the selected subset at a substantially the same second time.

[0066] The apparatus may additionally be for determining the physical
state of cable lines in the network and may therefore include a state
determining means configured to determine the physical state of cable
lines in the network using the transmitter coupling units and the
receiver coupling units as described above.

[0067] The first aspect of the invention may provide a method including
method steps corresponding to the use of an above described apparatus.

[0068] The interconnection identification means may include:

[0069] at least one signal generating unit configured to generate the test
signal; and

[0070] conveying means configured to convey the test signal generated by
the at least one signal generating unit to the plurality of transmitter
coupling units.

[0071] The conveying means may include at least one splitter unit
configured to receive the test signal via a single input signal path from
the signal generating unit and to output the test signal via a plurality
of output signal paths. Thus, the splitter unit provides a simple means
to allow the conveyance of the same test signal to a plurality of the
transmitter coupling units at the same time.

[0072] Each output signal path of the at least one splitter unit may
include a respective switch operable to control whether a test signal is
outputted via the output signal path and/or a balun. The switches may
provide a convenient means for conveying the test signal only to a subset
of the transmitter coupling units. Each switch (in the at least one
splitter unit) may be a switchable amplifier. This helps to reduce the
creation of reflections in the output signal path.

[0073] The conveying means may include at least one further splitter unit
configured to receive the test signal via a single input signal path from
the output signal path of a splitter unit and to output the test signal
via a plurality of output signal paths (e.g. directly to electrodes of a
transmitter coupling unit). Splitting an already split test signal in
this way provides a simple means to allow the conveyance of the same test
signal to a plurality of the transmitter coupling units at the same time.

[0074] Each output signal path of the at least one further splitter unit
may include a respective switch operable to control whether a test signal
is outputted via the output signal path and/or a balun. The switches may
provide a convenient means for conveying the test signal only to a subset
of the transmitter coupling units. To reduce cost, each switch (in the at
least one further splitter unit) may be an analogue switch, preferably an
analogue switch having a high "off" isolation. Reducing reflections in
the at least one further splitter unit may not be as important as
reducing reflections in the at least one splitter unit.

[0075] One or more (preferably all) of the splitter units and/or further
splitter units may include a test signal detector for detecting a test
signal from the at least one signal generating unit. The or each test
signal detector may be a radio frequency detector. The or each radio
frequency detector may comprise an arrangement including a diode, a
resistor and a capacitor.

[0076] The interconnection identification means may be configured to
identify interconnections between the signal generating unit, the
splitter units and/or the further splitter units by generating test
signals using the signal generating unit and detecting the test signals
using one or more of the test signal detectors.

[0077] The conveying means may include switching means operable to control
which of the plurality of transmitter coupling units receives the test
signal from the signal generating unit. The switching means may therefore
include: a respective switch located in each output signal path of at
least one splitter unit; and/or a respective switch located in each
output signal path of at least one further splitter units, as described
above.

[0078] The interconnection identification means may include:

[0079] a signal analysing unit for analysing a test signal coupled out
from a cable line by one of the plurality of receiver coupling units; and

[0080] conveying means configured to convey a test signal coupled out from
a cable line by one of the plurality of receiver coupling units to the
signal analysing unit.

[0081] The conveying means may include switching means operable to couple
any one of the plurality of receiver coupling units to the signal
analysing unit via a signal path which is common to all receiver coupling
units.

[0082] The switching means may include a respective switch located between
each receiver coupling unit and the common signal path.

[0083] In a second aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0084] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0085] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0086] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0088] at least one signal generating unit configured to generate the test
signal; and

[0089] conveying means configured to convey the test signal generated by
the at least one signal generating unit to the plurality of transmitter
coupling units;

[0090] wherein the conveying means includes at least one splitter unit
configured to receive the test signal via a single input signal path from
the signal generating unit and to output the test signal via a plurality
of output signal paths.

[0091] The apparatus may have any feature described in connection with the
first aspect of the invention, e.g. at least one further splitter unit,
e.g. switching means. Thus, the second aspect of the invention may
provide an apparatus including such features, but without necessarily
including an interconnection identification means as set out in the first
aspect of the invention.

[0092] In a third aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0093] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0094] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0095] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0097] at least one signal generating unit configured to generate the test
signal; and

[0098] conveying means configured to convey the test signal generated by
the at least one signal generating unit to the plurality of transmitter
coupling units;

[0099] wherein the conveying means includes:

[0100] at least one splitter unit configured to receive the test signal
via a single input signal path from the signal generating unit and to
output the test signal via a plurality of output signal paths;

[0101] optionally, at least one further splitter unit configured to
receive the test signal via a single input signal path from the output
signal path of a splitter unit and to output the test signal via a
plurality of output signal paths;

[0102] wherein one or more (preferably all) of the splitter units and/or
further splitter units includes a test signal detector for detecting a
test signal from the at least one signal generating unit.

[0103] The apparatus may have any feature described in connection with the
first aspect of the invention, e.g. the interconnection identification
means and/or state determining means may be configured to identify
interconnections between the signal generating unit, the splitter units
and/or the further splitter units by generating test signals using the
signal generating unit and detecting the test signals using one or more
of the test signal detectors. Thus, the third aspect of the invention may
provide an apparatus including such features, but without necessarily
including an interconnection identification means as set out in the first
aspect of the invention.

[0104] In a fourth aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0105] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0106] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0107] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0109] a signal analysing unit for analysing a test signal coupled out
from a cable line by one of the plurality of receiver coupling units; and

[0110] conveying means configured to convey a test signal coupled out from
a cable line by one of the plurality of receiver coupling units to the
signal analysing unit;

[0111] wherein the conveying means includes switching means operable to
couple any one of the plurality of receiver coupling units to the signal
analysing unit via a signal path which is common to all receiver coupling
units.

[0112] The apparatus may have any feature described in connection with the
first aspect of the invention, e.g. the switching means may include a
respective switch located between each receiver coupling unit and the
common signal path. Thus, the fourth aspect of the invention may provide
an apparatus including such features, but without necessarily including
an interconnection identification means as set out in the first aspect of
the invention.

[0113] In a fifth aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0114] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0115] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0116] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0118] at least one signal generating unit configured to generate the test
signal; and

[0119] a wander lead for coupling, via an additional transmitter coupling
unit, the test signal generated by the at least one signal generating
unit into any one of the cable lines in a network comprising a plurality
of cable lines.

[0120] The wander lead may include or be coupled to the additional
transmitter coupling unit.

[0121] In a sixth aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0122] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0123] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0124] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0125] wherein the interconnection identification means and/or state
determining means includes at least one signal generating and/or
analysing unit configured to generate the test signal and/or analyse a
test signal coupled out by one of the plurality of receiver coupling
units;

[0126] wherein the at least one signal generating and/or analysing unit
includes a synch block which allows the signal generating and/or
analysing unit to be synchronised with other signal generating and/or
analysing units.

[0127] Synchronising the signal generating and/or analysing unit is
useful, for example, in using multiple signal generating units to
generate the same test signal at substantially the same time, e.g. as may
be useful in connection with the first aspect of the invention.

[0128] In a seventh aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0129] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0130] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0131] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0132] wherein the interconnection identification means and/or state
determining means includes at least one cable including a plurality of
twisted pairs, wherein the interconnection identification means is
configured such that:

[0133] a first twisted pair in the at least one cable carries a test
signal generated by a signal generating unit; and/or

[0134] a second twisted pair in the cable carries a first communications
signal for providing information from one component in the
interconnection identification means and/or state determining means to
another component in the interconnection identification means and/or
state determining means; and/or

[0135] a third twisted pair in the cable carries a second communications
signal for providing information from one component in the
interconnection identification means and/or state determining means to
another component in the interconnection identification means and/or
state determining means, wherein the second communications signal
propagates in a direction opposite to that of the first communications
signal; and/or

[0136] a fourth twisted pair in the cable carriers power for powering one
or more components of the interconnection identification means.

[0137] The interconnection identification means and/or state determining
means may include a signal generating unit configured to generate the
test signal.

[0138] The communication signal(s) may be transmitted, for example,
according to the RS485 standard. The components between which
communication signals may be transmitted may include, for example, a
signal generating and/or analysing unit configured to generate the test
signal and/or analyse a test signal coupled out by one of the plurality
of receiver coupling units; a splitter unit; and/or a further splitter
unit.

[0139] In an eighth aspect, the invention may provide an apparatus for
identifying interconnections in a network comprising a plurality of cable
lines and/or for determining the physical state of cable lines in the
network, the apparatus having:

[0140] a plurality of transmitter coupling units, each transmitter
coupling unit being configured to couple to a respective cable line in a
network comprising a plurality of cable lines and to couple a test signal
into the respective cable line;

[0141] a plurality of receiver coupling units, each receiver coupling unit
being configured to couple to a respective cable line in the network and,
if a test signal is present in the respective cable line, to couple the
test signal out from the respective cable line;

[0142] wherein the apparatus includes an interconnection identification
means configured to identify interconnections between the transmitter
coupling units and the receiver coupling units by cable lines in the
network and/or a state determining means configured to determine the
physical state of cable lines in the network using the transmitter
coupling units and the receiver coupling units;

[0143] wherein the interconnection identification means and/or state
determining means is configured to perform an installation sequence in
which each transmitter coupling unit and each receiver coupling unit is
associated with a respective port in the network.

[0144] The interconnection identification means may further be configured
to record in a database the association of each transmitter coupling unit
and each receiver coupling unit with a respective port in the network.

[0145] The installation sequence may, comprise, for example:

[0146] (i) supplying prompts to a user;

[0147] (ii) manual inputting of data by the user in response to the
prompts.

[0148] In an ninth aspect, the invention may provide a coupling unit for
coupling a voltage signal to and/or from a cable including a plurality of
twisted pairs, the coupling unit having:

[0149] a first electrode and a second electrode arranged to produce an
electric field therebetween to couple a voltage signal to the cable by
non-contact coupling with the twisted pairs so that the voltage signal
propagates along the cable between at least two of the twisted pairs
and/or arranged to receive a voltage signal which has propagated along
the cable between at least two of the twisted pairs by non-contact
coupling with at least two of the twisted pairs between which the voltage
signal has propagated;

[0150] wherein the first and/or second electrodes of the coupling unit are
located (preferably printed) on a flexible circuit board.

[0151] The flexible circuit board provides a convenient means of providing
electrodes which can easily be pressed against the sleeve of a twisted
pair cable.

[0152] The first and second electrodes may be located (preferably printed)
on one side of the flexible circuit board. A ground plane may be located
(preferably printed) on an opposite side of the flexible circuit board to
the first and second electrodes. This arrangement helps provide shielding
for the first and second electrodes.

[0153] The flexible circuit board may have a comb (e.g. ctenoid) shape,
with a plurality of projections forming the comb shape. The first and
second electrodes of the coupling unit are preferably located (preferably
at a distal end) on a projection of the comb shape.

[0154] The coupling unit may have a third electrode and a fourth electrode
arranged to produce an electric field therebetween to couple a voltage
signal to the cable by non-contact coupling with the twisted pairs so
that the voltage signal propagates along the cable between at least two
of the twisted pairs and/or arranged to receive a voltage signal which
has propagated along the cable between at least two of the twisted pairs
by non-contact coupling with at least two of the twisted pairs between
which the voltage signal has propagated. In this case, the third and
fourth electrodes may be located on a projection of the comb shape that
is different to that on which the first and second electrodes of the
coupling unit are mounted.

[0155] The pairs of electrodes from other coupling units may also be
located on other projections of the comb shape.

[0156] The coupling unit may include a clip made of resilient/elastic
material (e.g. plastic), the clip being configured to press the first and
second electrodes (and optionally the third and fourth electrodes) of the
coupling unit against the sleeve of a twisted pair cable.

[0157] The flexible circuit board may include conductive pads for
connecting the first and second electrodes (and optionally the third and
fourth electrodes) to corresponding pads on an external circuit board.

[0158] The flexible circuit board may be configured to be connected to the
external circuit board by clamping the conductive pads of the flexible
circuit board against the corresponding pads of the external circuit
board.

[0159] The coupling unit may be for use with any apparatus for identifying
interconnections in a network comprising a plurality of cable lines
and/or for determining the physical state of cable lines in the network,
e.g. as described herein.

[0160] Any interconnection identification means and/or state determining
means described herein may include at least one signal generating unit
configured to generate the test signal and/or at least one signal
analysing unit configured to analyse a test signal coupled out by one of
the plurality of receiver coupling units. A signal generating unit and an
analysing unit may be provided by a single unit, which unit may be
referred to e.g. as a "scanner".

[0161] In any apparatus for identifying interconnections in a network
comprising a plurality of cable lines and/or for determining the physical
state of cable lines in the network described herein, each transmitter
coupling unit may be configured to couple a test signal into a respective
cable line in the network such that the test signal propagates along the
respective cable line between at least two conductors in the respective
cable line. The at least two conductors in the respective cable line may
be twisted pairs in the cable line. Thus, each transmitter coupling unit
may be configured to couple a test signal into a respective cable line in
the network such that the test signal propagates along the respective
cable line between at least two twisted pairs in the respective cable
line.

[0162] Equally, in any apparatus for identifying interconnections in a
network comprising a plurality of cable lines and/or for determining the
physical state of cable lines in the network described herein, each
receiver coupling unit may be configured to couple a test signal out from
a respective cable line in the network after it has propagated between at
least two conductors in the respective cable line. The at least two
conductors in the respective cable line may be twisted pairs in the cable
line. Thus, each receiver coupling unit may be configured to couple a
test signal out from a respective cable line in the network after it has
propagated between at least two twisted pairs in the respective cable
line.

[0163] In any apparatus for identifying interconnections in a network
comprising a plurality of cable lines and/or for determining the physical
state of cable lines in the network described herein, each transmitter
coupling unit may be configured to couple a test signal into a respective
cable line in the network by non-contact coupling with conductors in the
respective cable line. Equally, each receiver coupling unit may be
configured to couple a test signal out from a respective cable line in
the network by non-contact coupling with the conductors in the respective
cable line. In this context, non-contact coupling refers to coupling that
does not involve direct electrical (i.e. ohmic) contact with the
conductors of the cable line.

[0164] Coupling units capable of coupling a test signal into (or out from)
a twisted pair cable line so that the signal propagates (or after the
signal has propagated) between at least two twisted pairs in the twisted
pair cable line by non-contact coupling are disclosed, for example, in UK
patent application number GB2468925, US2011/0181374 and WO2010/109211,
and also in UK patent application number GB1009184.1, a copy of which is
annexed hereto.

[0165] Accordingly, in any apparatus for identifying interconnections in a
network comprising a plurality of cable lines and/or for determining the
physical state of cable lines in the network described herein, each
transmitter coupling unit may include any one or more of the following
features: first and second electrodes arranged to produce an electric
field therebetween to couple a voltage signal (which may, for example, be
a test signal generated by a signal generating unit) into a twisted pair
cable by non-contact coupling with twisted pairs in the twisted pair
cable so that the voltage signal propagates along the twisted pair cable
between at least two of the twisted pairs; electrical isolation means
(e.g. a balun) arranged to electrically isolate the electrodes from the
signal generating unit; shielding for shielding the electrodes from an
external electromagnetic field; means for converting (e.g. a choke) a
single-ended voltage signal from a signal generating unit into a
differential voltage signal to be coupled to the electrodes; and a
housing which may be arranged to be clipped onto a twisted pair cable.

[0166] Likewise, in any apparatus for identifying interconnections in a
network comprising a plurality of cable lines and/or for determining the
physical state of cable lines in the network described herein, the or
each receiver coupling unit may include any one or more of the following
features: first and second electrodes arranged to couple a voltage signal
(which may, for example, be a test signal that was coupled into one of
the plurality of cable lines by a transmitter coupling unit) out from a
twisted pair cable by non-contact coupling with at least two of the
twisted pairs in the twisted pair cable between which the voltage signal
has propagated; electrical isolation means (e.g. a balun) arranged to
electrically isolate the electrodes from the signal processing unit;
shielding for shielding the electrodes from an external electromagnetic
field; means for converting (e.g. a choke) a differential voltage signal
from the electrodes into a single-ended voltage signal to be coupled to a
signal processing unit; a housing which may be arranged to be clipped
onto a twisted pair cable.

[0167] Any test signal described herein may be a signal having
characteristics such that, when it is coupled out from a cable line by a
receiver coupling unit, the characteristics of the test signal can be
analysed to determine whether the resulting second test signal has
propagated directly to the receiver coupling unit from a transmitter
coupling units. The present inventors have found that signals suitable
for performing time domain reflectometry or frequency domain
reflectometry are suitable for such purposes. Accordingly, a test signal
described herein may be a test signal suitable for performing time domain
reflectometry and/or a first test signal suitable for performing
frequency domain reflectometry, which may be a voltage signal.

[0168] In time domain reflectometry, a system response is measured as a
function of time. A test signal suitable for time domain reflectometry
might be, for example, an impulse or narrow transient test signal, e.g.
having a duration of less than 10 ns (which corresponds to an electrical
length of 2 metres).

[0169] In frequency domain reflectometry, a system response is measured as
a function of frequency. A test signal suitable for frequency domain
reflectometry might be, for example, a frequency swept sine wave or
pseudo random noise. Frequency domain information can be converted into a
corresponding time domain response via an inverse Fourier transform, as
would be known to those skilled in the art.

[0170] In any apparatus for determining the physical state of cable lines
in a network described herein, a state determining means may be
configured to determine the physical state of a cable line in the network
e.g. by coupling a test signal into a selected cable line using one of
the transmitter coupling units, coupling a test signal out of the
selected cable line using one of the receiver coupling units and
analysing, e.g. in a signal analysing unit, the test signal coupled out
of the selected cable line by the receiver coupling unit so as to
determine a physical state of the cable. For example, the physical state
of the cable line may be determined by comparing a received test signal
with a reference test signal, as is known in the art of reflectometry. An
apparatus for determining the physical state of cable lines in a network
is shown, for example, in FIG. 3.

[0171] Herein, the term "cable" preferably refers to any cable capable of
carrying a signal, e.g. a voltage signal or an optical signal. The term
"cable line" preferably refers to either a cable or a plurality of cables
connected together so as to be capable of carrying a signal. In some
embodiments, the term "cable" may refer to a cable including at least two
conductors. In some embodiments, the term "cable line" may refer to
either one such cable or to a plurality of such cables whose conductors
have been directly, i.e. by direct electrical ("ohmic") contact, coupled
together.

[0172] Herein, when it is described herein that a signal propagates
"between" at least two conductors in a cable line, it is meant that the
signal propagates along the cable line due to a coupling between the
conductors, the signal being difference in state between the conductors.
Such a signal is commonly referred to as "differential" signal. A
differential signal is therefore distinguished from a so-called "common
mode" signal, where all the conductors have substantially the same state
and the signal is a difference in state between all the conductors and an
external reference (e.g. ground).

[0173] For example, a signal that propagates between at least two
conductors in a cable line may be a voltage signal, i.e. a difference in
voltage between at least two conductors in the cable line, which
propagates along the cable line due to inductive and capacitive coupling
between at least two conductors. Here, the capacitance per metre and
inductance per metre will generally determine e.g. the speed of
propagation of such a voltage signal.

[0174] For the avoidance of doubt, when a signal is described herein as
propagating along a cable line, the signal does not have to propagate
along the entire length of the cable line. Likewise, when a signal is
described herein as having propagated along a cable line, the signal does
not have to have propagated along the entire length of the cable line.

[0175] In another aspect of the invention, there may be provided a kit of
parts for forming an apparatus as set out in any above aspect, e.g. an
apparatus for identifying interconnections in a network comprising a
plurality of cable lines and/or for determining the physical state of
cable lines in the network. The kit of parts may include, for example, a
plurality of transmitter coupling units, and/or a plurality of receiver
coupling units, and/or an interconnection identification means, and/or a
state determining means as set out above and/or subcomponents thereof.

[0176] In another aspect of the invention, there may be provided any
component of an apparatus as set out in any above aspect, e.g. an
apparatus for identifying interconnections in a network comprising a
plurality of cable lines and/or for determining the physical state of
cable lines in the network. The component may be, for example, a
transmitter coupling unit, a receiver coupling unit, an interconnection
identification means or a state determining means as set out above, or a
subcomponent thereof.

[0177] In another aspect of the invention, there may be provided a method
which may include any method step corresponding to the use of any
apparatus or apparatus feature described in connection with any above
aspect of the invention.

[0178] The invention also includes any combination of the aspects and
preferred features described except where such a combination is clearly
impermissible or expressly avoided.

[0179] Examples of our proposals are discussed below, with reference to
the accompanying drawings in which:

[0180] FIG. 1 shows a typical patch system organised into a server row, a
cross-connect row and a network row.

[0181]FIG. 2 is a block diagram of a system configured to determine
interconnection status such as a map of the patch leads with a local area
network.

[0182]FIG. 3 is a block diagram of a system configured to monitoring the
physical status of the channels within the network. It will be apparent
to one skilled in the art that an apparatus could be configured to have
the functionality of the systems shown in both FIG. 2 and FIG. 3. The two
functions have been illustrated in separate drawings in this application
for clarity.

[0183]FIG. 4 is a representation illustrating the main component blocks
contained with the "Scanners" shown in FIGS. 2 and 3.

[0184]FIG. 5 is a representation of the main circuit blocks contained in
the "24 way splitter" shown in FIGS. 2 and 3.

[0185]FIG. 6 is a representation the interconnection details between the
"24 way splitter" and the "Tx front end units".

[0186]FIG. 7 is a representation of the main circuit blocks contained in
the "Tx Front End units" shown in FIGS. 2 and 3.

[0187]FIG. 8 is a representation of the main circuit blocks contained in
the "Rx Front End units" shown in FIGS. 2 and 3.

[0188] FIGS. 9(a)-(d) are representations showing the use of flexible
printed circuit for implementing the transmitter and/or receiver plates.

[0189]FIG. 10 is a representation showing how the transmitter and/or
receiver plates can be clipped around the cable in a format that can be
easily deployed in the field.

[0190] FIGS. 2 and 3 show block diagrams for the system hardware. The
system preferably has two main modes of operation in which FIG. 2 shows
the system operating in a "patching" mode, whereby the system determines
a connectivity map of the patch cable, which the user has inserted in
between the patch panels to configure the local area network. FIG. 3
shows the system operating in a "monitoring" mode whereby the system
inspects each channel on the network e.g. by performing reflectometry to
look for impedance changes in each channel. Any impedance changes may
indicate a change in status of the channel such as a fault in the cable
or a unit being unplugged at the end of the channel. The system is
preferably controlled by a host PC, which is connected to one or more
scanner units. In this example, Ethernet, which is labelled IP, is used
to provide communications between each scanner unit and the host PC. The
host PC preferably reports information about the network and receives
instructions over the Internet, labelled as the Cloud. The system may be
controlled by programmes which are either local on the host PC or hosted
on external resources in the Cloud via external service providers.

[0191] Referring to FIG. 2, the system preferably determines a
connectivity map by applying a test signal to one or more transmitter
coupling units, which are labelled "Tx plates", and then monitors the
signal from one or more receiver coupling units, labelled "Rx plates".
The transmitter coupling units and the receiver coupling units may
typically be placed directly behind the patch panels. An adequate number
coupling units is preferably used such that a full connectivity map
between all relevant ports can be determined by the system. Any test
signal received by the Rx plates is preferably analysed by signal
processing algorithms, such as those described in GB1009184.1, to
determine if the signal has been conveyed directly between the
transmitter coupling unit and the receiver coupling unit, in which case
there is a patch lead present, or via an unwanted route, such as alien
crosstalk between UTP cables in the network. The system preferably
implements a search algorithm to determine all the directly conveyed
signal paths between every transmitter coupling unit and every receiver
coupling unit. Each directly conveyed signal path is evidence of a patch
lead connected between the respective ports. The search algorithm
preferably ensures that all possible patch lead positions are examined in
an efficient manner. One possible search algorithm is a binary tree in
which half the possible interconnections from the ports with transmitter
coupling units a port with a receiver coupling unit are tested first; if
the result shows no direct connection then the other half of the possible
interconnections are tested; if the result shows no direct connection
then no patch lead is present; alternatively if a direct connection is
detected on either half, then the algorithm tests one quarter of the
remaining possible interconnections; then one eight etc until the
presence of a interconnection or not has been established. It should be
noted that there are many variations on this theme and although a binary
tree search is thought to be the most efficient, any structured and
logical search may in practice be performed by the system to ensure that
all possible direct connections are determined.

[0192] In order to apply the test signal to one or more transmitter
coupling units, the system preferably contains as series of splitters and
Tx front end coupling couplings, which contain switches or switched
amplifiers as appropriate to convey the test signal to one or any
combination of transmitter coupling units as required. The internal
operation of the splitter and Tx front end units are shown in FIGS. 5 and
7 respectively. In addition, the scanner may provide an output for a
wander lead, which might simply be a transmitter coupling unit on a free
lead. The wander lead may be hand held or attached to any accessible
cable in the network as required by the user to test the connectivity of
a particular port or cable.

[0193] The structure of UTP is such that the individual twisted pairs are
held together by a sleeve. Within the sleeve, the bundle of twisted pairs
is also twisted by the manufacturers with an overall twist rate, with a
value denoted here as lambda. It is highly preferable to ensure that both
the transmitter coupling units and receiver coupling units are positioned
next to the same corresponding pairs inside the sleeve of the UTP cable.
Unfortunately, the sleeve is usually not transparent and consequently the
correct position of the coupling units cannot easily be determined. To
overcome this problem two transmitter coupling units are preferably
deployed on each cable as shown. The two transmitter coupling units are
preferably aligned in the same radial direction, but preferably spaced by
lambda/4, which helps to ensure that one of the two coupling units will
have good coupling to the corresponding pairs under the appropriate
receiver coupling unit.

[0194] The signal received by any receiver coupling unit can be conveyed
back to a scanner by a switching network contained in the Rx front end
units and a radio frequency bus, such as a coaxial cable, labelled Rx
coax. The internal operation of an Rx front end unit and its connection
to the Rx coax is shown in FIG. 8.

[0195] The scanner units typically have the provision to service several
splitter units and several Rx coax buses with multiple inputs and outputs
of these types. This helps to ensure that a moderately sized network,
such as one containing 500 ports can have the patch lead connectivity map
determined with a single controller unit. For larger networks, multiple
controller units may be needed in which case the timing of the signal
capture and processing operation must be synchronised. Synchronisation
can be achieved using dedicated connections between the scanner units.
Typically one scanner unit will be programmed or configured to serve as
the master and provide the necessary synchronisation signal to the other
scanner units.

[0196] Communication between the scanner and the associated splitter and
front end units is preferably achieved with a communication bus. A serial
bus such as RS485 is a convenient means of implementing this
communication as this can be connected in a daisy chain fashion around
the respective units.

[0197] It should be noted that the architecture of FIG. 2 is preferably
such that the delay that the transmitter test signal encounters from the
scanner to the transmitter coupling units are approximately the same for
all transmitter coupling units assuming that similar cable lengths are
used for corresponding paths in the system. This helps to ensure that
directly connected paths in the network are easy to identify by the
signal processing algorithms later.

[0198]FIG. 3 shows the operation of the system when operating in the
"monitoring" mode. Here only the relevant system block as shown. The
monitoring functionality is preferably achieved using reflectometry.
Reflectometry is an established technique which is well known by those
skilled in the art of signal processing. Reflectometry can be implemented
in a number of ways such as time domain reflectometry, frequency domain
reflectometry and the like. The chosen method for this system is to
perform reflectometry in the frequency domain, however other approaches
are viable. Consequently, the scanner units preferably generate a test
signal consisting of a wide band sweep of frequencies from 1 to 100 MHz,
which typically contain 128 or 256 individual frequency values, which may
be equally spaced. A similar test signal may also used for the "patching"
mode described earlier.

[0199] The system preferably implements reflectometry by using a
transmitter coupling unit to transmit the reflectometry signal and a
receiver coupling unit to receive the reflectometry signal. The two
coupling units are preferably positioned at integer multiplies of
lambda/2 to ensure adequate coupling to the same twisted pairs inside the
sleeve of the UTP cable in a similar manner to that described earlier for
"patching" mode. The system can be economically implemented using a
transmitter coupling units and receiver coupling units in combinations to
connect to their respective coupling units behind each patch panel. The
association of pairs of transmitter and receiver front end units may be
controlled using direct RS485 communications between them.

[0200]FIG. 4 shows a block diagram of the internal components inside a
scanner unit. The scanners preferably contain a processor in this case a
moderately powerful microcontroller, labelled μC, which communicates
with the host PC via Ethernet and the splitter, Rx front end and Tx front
end units using RS485. The microcontroller preferably contains the
programmes necessary to control the units responsible for signal
generation and signal acquisition. The circuit preferably used to
synchronise scanner units is also shown. The synchronisation circuits
help to ensure that the multiple scanner units can operate at the same
clock frequency and that time critical signal acquisition and signal
process function occur simultaneously. For example the synchronisation
helps to ensure phase coherence during the capture and demodulation of
the frequency sweeps. The signal processing functions such as digital
demodulation is preferably performed by the field programmable gate array
(FPGA). The FPGA controllers the signal generator, which is preferably a
direct digital synthesiser (DDS), and which preferably generates the
frequency sweep test signals described earlier. The DDS also preferably
generates the reference frequency (f-fIF) for the multiplier. The
reference frequency is preferably offset by a fixed value to representing
the intermediate frequency in the heterodyne demodulation scheme. The
output from the DDS is also preferably conveyed to one or more outputs
for the splitter and Tx front end units described earlier. Switchable
amplifiers with enable lines (EN) are preferably used to select to
activate the appropriate transmitter output on the scanner unit in order
to convey the transmitter signal to the rest of the system as required.
Twisted pair is preferably used as a convenient and low cost transmission
medium for the transmitter signals. Baluns may also be added to help
reduce the common mode signal applied the twisted pairs, which helps to
minimise crosstalk in the system.

[0201] The signal capture scheme may consist of a relatively standard
heterodyne demodulation method. The signal input is preferably conveyed
to an analogue demodulator which contains a multiplier and a low pass
filter as is common practice for such demodulators. The offset in
frequency between the input signal and reference preferably results in a
signal at the input to the analogue to digital converter (ADC) with a
frequency of fIF. The ADC signal preferably digitises this signal
and the FPGA preferably implements a digital demodulation algorithm to
determine the in-phase and quadrature values of the signal at each value
of frequency contained in the frequency sweep. The scanner preferably
uses a multiplier arrangement to select one of several possible receiver
signals. The receiver signals are preferably relatively small and
preferably require amplification and should be conveyed to the scanner
using a good quality transmission medium such as coaxial cable.

[0202]FIG. 5 shows the internal circuitry of the splitter unit, which may
contain 24 outputs. All signal lines are preferably differential. The
input signal, RF In is preferably passed first passed through a balun to
reject common mode signal components and then a buffer preferably helps
to ensure that the input signal line is correctly matched to the input
impedance of the splitter unit. Similarly output baluns and buffers
amplifiers are preferably used to help minimise common mode interference
in the system and match to the output lines, RF Out 1, RF Out 2, RF Out
3, etc. respectively. The output buffers are preferably of a switchable
type such that their outputs can be switched on or off by the
corresponding enable line, EN1, EN2, EN3 etc. A low power microcontroller
such as a PIC type with an RS485 interface can be used to activate the
appropriated RF Out lines as required by commands send along the RS485
bus. The splitter preferably also contains components for DC power
management and LEDs for indication of functionality to the user, but
these miscellaneous and ancillary components are not shown, which is the
case for the main sub-units described in this document.

[0203]FIG. 6 contains an illustration of the routing of the lines for the
RF transmitter signals, the RS485 communications serial communications
bus, and the two DC power levels between the splitter unit and the Tx
front end units. In this particular system, UTP and RJ45 connectors have
been used as a convenient and economical means of conveying these lines.
As shown, one UTP cable containing 4 twisted pairs can convey the RS485,
signal and power lines, with the RS485 connected following a daisy chain
path out and back between the splitter unit and the Tx front end units.
This connection scheme preferably requires that the RJ45 connectors (Tx
FE1, Tx FE2, etc in FIG. 2) are populated in a strict sequence to ensure
continuity of the RS485 line through all the transmitter front end units.
In addition a 100 ohm termination is preferably be inserted in the first
free Tx FE socket to help ensure that the RS485 bus is correctly
terminated, thereby avoiding unwanted reflections and corrupted data.

[0204]FIG. 7 depicts the operation of a transmitter front end unit. This
is similar in nature to the splitter unit shown in FIG. 5 and previously
described earlier. For the purposes of brevity only the essential
differences will be described. First analogue switches are preferably
used at the output as a lower cost and lower power alternative to
switchable amplifiers. The outputs of the transmitter front end unit are
preferably fed directly via short leads, typically 10 cm to the plates in
the transmitter coupling units. Consequently such short leads do not need
driving with buffer amplifiers. Second, the transmitter front end unit is
preferably made in section of 12 channels for convenience as many patch
panels are 24 ports wide. The multiple of 12 allows the signal to be fed
into the middle of the Tx FE signal to feed into a connector positioned
in the middle of the unit. Third the transmitter front end unit
preferably contains 48 output channels this is to accommodate to coupling
units per cable on a 24 port patch panel. Four, a simple RF detect
signal, typically consisting of a diode, resistor and capacitor is
preferably used to detect when a transmitter signal has been applied to
the RF In input. This is used later in the installation sequence to
detect which transmitter front end units are connected to which outputs
on the splitter and determine coincidence between their corresponding
individual addresses stored on the programmes on each of the PIC
microcontrollers.

[0205]FIG. 8 shows the architecture of a receiver front end unit. There
are structural similarities between the converse functions on the
transmitter side described for the splitter unit in FIG. 5 and the
transmitter front end unit in FIG. 7. Therefore for brevity only the key
functional differences will be described here. First, of course the
signal flow is in the opposite direction. Baluns are an useful feature on
the input to help to ensure that the common mode signal is rejected and
mainly the desired component, such as the pair to pair component is
conveyed to the following stages. Second, amplifiers are useful at the
input to both amplify the signal and present the required input impedance
to the receiver coupling unit. The amplifiers preferably have switchable
outputs such that the required receiver coupling unit signal is conveyed
to the output. Clearly only one or no input amplifiers are enabled at a
time. At the output, the signal is preferably routed through a pair of
switch switches which serve a changeover function. This is typically a
good quality switch such as a screen RF reed relay to preserve the
integrity of transmission for signals on the Rx coax bus. The changeover
switch preferably either connects the signal from this receiver front end
unit to the Rx coax bus or passes the bus through to the next receiver
front end unit in the chain.

[0206] FIGS. 9(a)-(d) shows the construction of the coupling units. In
particular, FIG. 9(a) highlights the use of flexible printed board (PCB)
material such as polyimide as a convenient and inexpensive means of
realising the pair of plates required in either the transmitter coupling
unit or the receiver coupling unit. FIG. 9(b) show the view from the
plate (i.e. electrode) side and FIG. 9(c) is an illustration of the view
from the ground plane side. The ground plane serves an useful
electromagnetic screening role. FIG. 9(d) shows how the individual
elements for each coupling unit can be combined to form limbs of a comb
shape (ctenoid) structure for ease of connection to a rigid PCB. To avoid
a further soldering operation the metal conducting pads on the flexible
PCB can be pressed directly against corresponding aligned and positioned
conducting pads on the rigid PCB containing the circuitry for the
receiver front end unit.

[0207]FIG. 10 illustrates the design in schematic view of a compliant
elastic clip which may be used to press the plates on the flexible PCB
against the sleeve of the UTP cable. An end view of the clip is provided
here with the flexible PCB and the UTP cable in the middle.

[0208] When used in this specification and claims, the terms "comprises"
and "comprising" and variations thereof mean that the specified features,
steps or integers are included. The terms are not to be interpreted to
exclude the presence of other features, steps or integers.

[0209] The features disclosed in the foregoing description, or in the
following claims, or in the accompanying drawings, expressed in their
specific forms or in terms of a means for performing the disclosed
function, or a method or process for obtaining the disclosed results, as
appropriate, may, separately, or in any combination of such features, be
utilised for realising the invention in diverse forms thereof.

[0210] While the invention has been described in conjunction with the
exemplary embodiments described above, many equivalent modifications and
variations will be apparent to those skilled in the art when given this
disclosure, without departing from the broad concepts disclosed. It is
therefore intended that the scope of the patent granted hereon be limited
only by the appended claims, as interpreted with reference to the
description and drawings, and not by limitation of the embodiments
described herein.

ANNEX

Copy of UK Patent Application GB1009184.1

[0211] In this copy of UK patent application GB1009184.1, the figures have
been renumbered to avoid conflict with the other figures in this patent
application, and the claims have been relabelled as "statements" to avoid
confusion with the claims of this patent application.

Signal Processing Apparatuses and Methods

[0212] This invention relates to signal processing apparatuses and methods
for use with a plurality of cable lines, e.g. cable lines including one
or more twisted pair cables. In particular, this invention relates to
apparatuses and methods for analysing one or more characteristics of a
test signal coupled out from one of a plurality of cable lines. In some
examples, the invention relates to a network interconnection
identification apparatus for identifying interconnections between ports
in a network.

[0213] Cables which include a plurality of twisted pairs, referred to as
"twisted pair cables" herein, are well known. Such cables are commonly
used for telecommunications purposes, e.g. computer networking and
telephone systems. In the field of telecommunications, twisted pair
cables are usually provided without shielding, as unshielded twisted pair
(UTP) cables. However, shielded twisted pair (STP) cables are also known.

[0214] In this context, a "twisted pair" is a pair of conductors, usually
a forward conductor and a return conductor of a single circuit, which
have been twisted together. The conductors are usually twisted together
for the purposes of cancelling out electromagnetic interference from
external sources and to minimise crosstalk between neighbouring twisted
pairs within a cable comprising a plurality of twisted pairs. In this
way, each twisted pair provides a reliable respective communication
channel for a signal, usually a differential voltage signal, to be
conveyed within the twisted pair. Common forms of unshielded twisted pair
(UTP) cables are category 5 and category 6 UTP cables which include eight
conductors twisted together in pairs to form four twisted pairs.

[0215] The design and construction of twisted pair cables is carefully
controlled by manufacturers to reduce noise due to electromagnetic
interference and to reduce crosstalk between the twisted pairs within the
cables. To this end, each twisted pair in a twisted pair cable normally
has a different twist rate (i.e. number of twists per unit length along
the cable) from that of the other twisted pairs in the twisted pair
cable. It is also usual for the twisted pairs to be twisted around each
other within the cable. Fillets or spacers may be used to separate
physically the twisted pairs.

[0216] Networks including ports interconnected by a plurality of cables,
such as local area networks (LANs), are also well known. LANs are
typically used to enable equipment such as computers, telephones,
printers and the like to communicate with each other and with remote
locations via an external service provider. LANs typically utilise
twisted pair network cables, usually in the form of UTP cables.

[0217] The cables used in LANs are typically connected to dedicated
service ports throughout one or more buildings. The cables from the
dedicated service ports can extend through the walls, floor and/or
ceilings of the building to a communications hub, typically a
communications room containing a number of network cabinets. The cables
from wall and floor sockets within the building and from an external
service provider are also usually terminated within the communications
room.

[0218] A "patch system" may be used to interconnect various ports of the
LAN within the network cabinets. In a patch system, all cable lines in
the LAN can be terminated within the network cabinets in an organized
manner. The terminations of the cable lines in the network are provided
by the structure of the network cabinets, which are typically organised
in a rack system. The racks contain "patch panels", which themselves
utilise sets of ports, typically RJ-45 type connector ports, at which the
cable lines terminate.

[0219] Each of the ports in each patch panel is hard wired to one of the
cable lines in the LAN. Accordingly, each cable line is terminated on a
patch panel in an organized manner. In small patch systems, all cable
lines in the LAN may terminate on the patch panels of the same rack. In
larger patch systems, multiple racks are used, wherein different cable
lines terminate on different racks.

[0220] Interconnections between the various ports in the LAN are typically
made using "patch cables", which are usually UTP cables including four
twisted pairs. Each end of a patch cable is terminated by a connector,
such as an RJ-45 type connector for inserting into an RJ-45 type
connector port. One end of each patch cable is connected to the port of a
first cable line and the opposite end of the patch cable is connected to
the port of a second cable line. By selectively connecting the various
cable lines using the patch cables, a desired combination of network
interconnections can be achieved.

[0221] FIG. 22 shows a typical patch system organised into a server row
92, a cross-connect row 93 and a network row 94, which include patch
panels 96a, 96b, 96c, 96d. Patch cables 10a, 10b, 10c, 10d are used to
interconnect two ports through the patch system.

[0222] In many businesses, employees of a company are assigned their own
computer network access number so that the employee can interface with
the company's IT infrastructure. When an employee changes office
locations, it is not desirable to provide that employee with newly
addressed port in the network. Rather, to preserve consistency in
communications, it is preferred that the exchanges of the ports in the
employee's old office be transferred to the telecommunications ports in
the employee's new location. This type of move is relatively frequent.
Similarly, when new employees arrive and existing employees depart, it is
usually necessary for the patch cables in the network cabinet(s) to be
rearranged so that each employee's exchanges can be received in the
correct location.

[0223] As the location of employees change, the patch cables in a typical
cabinet are often manually entered in a computer based log. This is
burdensome. Further, technicians often neglect to update the log each and
every time a change is made. Accordingly, the log is often less than 100%
accurate and a technician has no way of reading where each of the patch
cables begins and ends. Accordingly, each time a technician needs to
change a patch cable, that technician manually traces that patch cable
between an internal line and an external line. To perform a manual trace,
the technician locates one end of a patch cable. The technician then
manually follows the patch cable until he/she finds the opposite end of
that patch cable. Once the two ends of the patch cable are located, the
patch cable can be positively identified.

[0224] It takes a significant amount of time for a technician to manually
trace a particular patch cable, especially in large patch systems.
Furthermore, manual tracing is not completely accurate and a technician
may accidently go from one patch cable to another during a manual trace.
Such errors result in misconnected patch cables which must be later
identified and corrected.

[0225] Attempts have been made in the prior art to provide an apparatus
which can automatically trace the common ends of each patch cable within
local area networks, thereby reducing the labour and inaccuracy of manual
tracing procedures.

[0226] For example, U.S. Pat. No. 5,483,467 describes a patching panel
scanner for automatically providing an indication of the connection
pattern of the data ports within a LAN, so as to avoid the manual task of
identifying and collecting cable connection information. In one
embodiment, which is intended for use with shielded twisted pair cables,
the scanner uses inductive couplers which are associated with the data
ports. The inductive coupler is disclosed as being operative to impose a
signal on the shielding of shielded network cables in order to provide an
indication of the connection pattern produced by connection of the cables
to a plurality of ports.

[0227] In another embodiment of U.S. Pat. No. 5,483,467, the scanner is
coupled to each data port by "dry contact" with a dedicated conductor in
a patch cable. This is difficult to implement in practice, because most
network cables have to meet a particular pre-determined standard in the
industry, such as the RJ-45 type standard, in which there is no free
conductor which could be used for determining interconnectivity.

[0228] U.S. Pat. No. 6,222,908 discloses a patch cable identification and
tracing system in which the connectors of each patch cable contain a
unique identifier which can be identified by a sensor in the connector
ports of a telecommunications closet. By reading the unique identifier on
the connectors of each patch cable, the system can keep track of which
patch chords are being added to and removed from the system. Although
this system avoids the use of dedicated conductors in the patch cable, it
is difficult to implement because it requires use of non-standard patch
cables, i.e. patch cables with connectors containing unique identifiers.

[0229] International Patent Application Publication Number WO00/60475
discloses a system for monitoring connection patterns of data ports. This
system uses a dedicated conductor which is attached to the external
surface of a network cable in order to monitor the connection pattern of
data ports. Although this allows the system to be used with standard
network cables, it still requires the attaching of dedicated conductors
to the external surfaces of network cables and adapter jackets which are
placed over the standard network cable.

[0230] U.S. Pat. No. 6,285,293 discloses another system and method for
addressing and tracing patch cables in a dedicated telecommunications
system. The system includes a plurality of tracing interface modules that
attach to patch panels in a telecommunications closet. On the patch
panels, are located a plurality of connector ports that receive the
terminated ends of patch cables. The tracing interface modules mount to
the patch panels and have a sensor to each connector port which detects
whenever a patch cable is connected to the connector port. A computer
controller is connected to the sensors and monitors and logs all changes
to the patch cable interconnections in an automated fashion. However,
this system cannot be retrofitted to an existing network and relies on
the operator to work in a particular order if the patch cable connections
are to be accurately monitored.

[0231] International Patent Application Publication Number WO2005/109015,
which relates to the field of cable state testing, discloses a method of
determining the state of a cable comprising at least one electrical
conductor and applying a generated test signal to at least one conductor
of the cable by a non-electrical coupling transmitter. The reflected
signal is then picked up and compared with expected state signal values
for the cable, so that the state of the cable can be determined. The
present inventors have found that signals coupled to a twisted pair cable
by the methods described in WO2005/109015 have a tendency to leak out
from the twisted pair cable, especially when other twisted pair cables
are nearby.

[0232] UK patent application number GB0905361.2, U.S. patent application
Ser. No. 11/597,575 and International patent application number
PCT/GB2010/000594, also by the present inventors, and the content of
which is herewith incorporated in its entirety, describe apparatuses and
methods for coupling a signal to and from a twisted pair cable by
non-contact coupling with twisted pairs in the twisted pair cable, such
that the signal propagates along the cable between at least two of the
twisted pairs. These methods and apparatuses related to a discovery by
the present inventors that a twisted pair cable provides communication
channels (referred to as "pair-to-pair channels") between the twisted
pairs within the twisted pair cable, these communication channels being
additional to the respective communication channel provided within each
twisted pair in the cable. In other words, a signal propagating between
the twisted pairs could be transmitted on a standard UTP cable (i.e. with
no specially adapted UTP cable needed) without interfering with signals
propagating within individual twisted pairs of the standard UTP cable.

[0233] "Crosstalk" is a common problem within the field of networks.
"Crosstalk" may be viewed as undesired signal coupling from one signal
channel to another. For networks including a plurality of twisted pair
cables, crosstalk may occur between the twisted pairs within individual
twisted pair cables, but most commonly occurs between twisted pairs in
different twisted pair cables, particularly when the twisted pairs have a
similar twist rate. In industry, crosstalk between different twisted pair
cables is sometimes referred to as "alien" crosstalk and is illustrated
by FIG. 11b, which is described in more detail below.

[0234] The presence of crosstalk between twisted pair cables can cause
serious difficulties for the operation of a network as it can cause
signals to be routed via undesired paths between ports in the network. To
address these difficulties, cables (e.g. category 5 and category 6 UTP
cables), connectors and associated components are normally manufactured
to ensure that levels of crosstalk are maintained within prescribed
standards. In addition, cables must often be installed and connected
according to guidelines in order to ensure that the network performs to
the prescribed standards.

[0235] The present invention has been devised in light of the above
considerations.

[0236] The present invention relates to a discovery by the present
inventors that the characteristics of a test signal coupled out from one
of a plurality of cable lines by a coupling unit are different depending
on whether that test signal has propagated directly to the coupling unit
via a single cable line or has propagated indirectly to the coupling unit
via one or more coupling paths between different cable lines. By
analysing one or more characteristics of such a test signal, the present
inventors have found that it is possible to determine whether the test
signal has propagated directly to the coupling unit via a single cable
line or has propagated indirectly to the coupling unit via one or more
coupling paths between different cable lines.

[0237] Accordingly, in general, the invention provides apparatuses and
methods for analysing at least one characteristic of a test signal
coupled out from one of a plurality of cable lines by a coupling unit to
determine whether that test signal has propagated directly to the
coupling unit via a single cable line or has propagated indirectly to the
coupling unit via one or more coupling paths between different cable
lines.

[0238] The determination of whether the test signal has propagated
directly to the coupling unit via a single cable line or has propagated
indirectly to the coupling unit via one or more coupling paths between
different cable lines, may advantageously be used for operational or
diagnostic purposes, e.g. to identify interconnections between ports in a
network.

[0239] Herein, for brevity, a test signal which has propagated directly
between a first coupling unit and a second coupling unit via a single
cable line is referred to as a "direct signal" and a signal which has
propagated between the first coupling unit and second coupling unit via a
coupling path extending between different cable lines is referred to as a
"crosstalk signal". As explained in more detail below, the present
inventors have found that a direct signal has different characteristics
(e.g. in the time and frequency domains) from a crosstalk signal. This
difference is illustrated, for example, by FIGS. 11a and 11b, which are
described in more detail below.

[0240] In a first aspect, the present invention provides a signal
processing apparatus as set out in statement A.

[0241] In other words, the signal processing apparatus is able to
distinguish between a direct signal and a crosstalk signal.

[0242] In this way, the signal processing apparatus is different from the
apparatuses described in UK patent application number GB0905361.2, U.S.
patent application Ser. No. 11/597,575 and International patent
application number PCT/GB2010/000594, also by the present inventors,
since the apparatuses described in these patent applications are not
configured to distinguish between these different types of signal.

[0243] Here, it should be appreciated that a determination by the signal
processing unit that condition (i) is true indicates that the first cable
line is also the second cable line. Likewise, it should be appreciated
that a determination by the signal processing unit that condition (ii) is
true indicates that the first cable line is different from the second
cable line.

[0244] Here, it should also be appreciated that the signal processing unit
may not be able to determine which of conditions (i) and (ii) is true for
each and every second test signal coupled out by the second coupling
unit. This might be the case, for example, if the second test signal does
not result from a first test signal coupled into a first cable line by
the first coupling unit. This might also be the case, for example, if the
signal processing unit needs to analyse the characteristics of a
plurality of second test signals, before it has enough information to
determine whether condition (i) or (ii) is true for any one or more of
those second test signals.

[0245] Herein, the term "cable" refers to a single cable including at
least two conductors. The term "cable line" refers to either one such
cable or to a plurality of such cables whose conductors have been
directly, i.e. by direct electrical (ohmic) contact, coupled together.

[0246] Herein, when it is described herein that a signal propagates
"between" at least two conductors in a cable line, it is meant that the
signal propagates along the cable line due to a coupling between the
conductors, the signal being difference in state between the conductors.
Such a signal is commonly referred to as "differential" signal. A
differential signal is therefore distinguished from a so-called "common
mode" signal, where all the conductors have substantially the same state
and the signal is a difference in state between all the conductors and an
external reference (e.g. ground).

[0247] For example, a signal that propagates between at least two
conductors in a cable line may be a voltage signal, i.e. a difference in
voltage between at least two conductors in the cable line, which
propagates along the cable line due to inductive and capacitive coupling
between at least two conductors. Here, the capacitance per metre and
inductance per metre will generally determine e.g. the speed of
propagation of such a voltage signal.

[0248] For the avoidance of doubt, when a signal is described herein as
propagating along a cable line, the signal does not have to propagate
along the entire length of the cable line. Likewise, when a signal is
described herein as having propagated along a cable line, the signal does
not have to have propagated along the entire length of the cable line.

[0249] The signal processing apparatus may include the plurality of cable
lines. The signal processing apparatus may include a network that
includes the plurality of cable lines. The network may include a
plurality of ports, which may be interconnected by the plurality of cable
lines.

[0250] Although the apparatus may have only one first coupling unit and
only one second coupling unit, the apparatus preferably includes a
plurality of first coupling units and/or a plurality of second coupling
units.

[0251] Preferably, the apparatus has a plurality of first coupling units,
each first coupling unit being configured to couple to a respective first
one of the plurality of cable lines and to couple a respective first test
signal generated by the signal generating unit into the respective first
cable line such that the respective first test signal propagates along
the respective first cable line between at least two conductors in the
respective first cable line.

[0252] Where there is a plurality of first coupling units, the first
coupling units are preferably configured to couple respective first test
signals generated by the test signal generating unit one at a time. In
this way, interference between test signals in the plurality of cable
lines, e.g. due to crosstalk, can be avoided. Also, coupling in first
test signals one at a time may help the signal processing unit to
determine which first coupling unit coupled in a first test signal that
resulted in one or more second test signals subsequently coupled out by a
plurality of second coupling units. Determining which first coupling unit
coupled in a first test signal that resulted in one or more second test
signals may be useful, for example, in helping the signal processing unit
to identify interconnections between ports in a network.

[0253] Preferably, the apparatus includes a plurality of second coupling
units, each second coupling unit being configured to couple to a
respective second one of the plurality of cable lines and, if a
respective second test signal is present in the respective second cable
line, to couple the respective second test signal out from the respective
second cable line.

[0254] Where there is a plurality of second coupling units, the signal
processing unit is preferably configured to, if any one or more of the
second coupling units couples out a respective second test signal,
analyse one or more characteristics of the or each respective second test
signal to determine, for at least one respective second test signal,
based on the one or more analysed characteristics, which of the following
conditions, if any, is true: (i) the respective second test signal is a
direct signal that has propagated directly from a first coupling unit to
a second coupling unit via a single cable line to which the first and
second coupling units are coupled; (ii) the respective second test signal
is a crosstalk signal that has propagated indirectly from a first
coupling unit to the second coupling unit via one or more coupling paths
between different cable lines to which the first and second coupling
units are respectively coupled.

[0255] Here, it should be appreciated that a determination that condition
(i) is true for a respective second test signal indicates that the
respective second test signal has resulted from a first test signal that
was coupled by a first coupling unit into a first cable line that is also
the second cable line from which the respective second test signal was
coupled out. Likewise, it should be appreciated that a determination that
condition (ii) is true for a respective second test signal indicates that
the respective second test signal has resulted from a first test signal
that was coupled by a first coupling unit into a first cable line that is
different from the second cable line from which the respective second
test signal was coupled out.

[0256] In some embodiments, the signal processing unit may be configured
to analyse only the one or more characteristics of a respective second
test signal to determine, for that second test signal, whether condition
(i) or (ii) is true. However, it is equally possible for the signal
processing unit to be configured to analyse one or more characteristics
of each of a plurality of respective second test signals to determine,
for one or more of the respective second test signals, whether condition
(i) or (ii) is true.

[0257] The determination by the signal processing unit of which, if any,
of conditions (i) and (ii) is true for a second test signal may
advantageously be used for operational or diagnostic purposes.

[0258] Preferably, the determination by the signal processing unit is used
to identify interconnections between ports in a network including a
plurality of cable lines. Accordingly, the test signal processing
apparatus is preferably implemented as a network interconnection
identification apparatus for identifying interconnections between ports
in a network including a plurality of cable lines. To this end, the
signal processing unit is preferably configured to, if it determines that
a second test signal coupled out by a second coupling unit is a direct
signal that has propagated directly from a first coupling unit to the
second coupling unit via a single cable line to which the first and
second coupling units are coupled, identify an interconnection between a
first port associated with that first coupling unit and a second port
associated with that second coupling unit. The or each first coupling
unit may be associated or associable with a respective first port in a
network and the or each second coupling unit may be associated or
associable with a respective second port in the network.

[0259] The signal processing unit may additionally or alternatively be
configured to, if it determines that a second test signal coupled out by
a second coupling unit is a crosstalk signal, measure the magnitude of
the crosstalk signal. The magnitude of the crosstalk signal could be
measured using techniques well known to those skilled in the art of
signal processing. The measured magnitude of the crosstalk signal could
be used, for example, to determine if there is too much crosstalk between
ports in a network. Too much crosstalk may be a symptom of cables running
too close to each other, and could therefore indicate to a network
operator that cables in the network need to be separated.

[0260] The first test signal generated by the signal generating unit may
be any signal having characteristics such that, when the first test
signal is coupled into one of a plurality of cables by a first coupling
unit, the characteristics of a resulting second test signal coupled out
from one of the plurality of cables by a second coupling unit can be
analysed to determine whether the resulting second test signal is a
direct signal or crosstalk signal. The present inventors have found that
signals suitable for performing time domain reflectometry or frequency
domain reflectometry are suitable. Accordingly, the signal generating
unit may be configured to generate a first test signal suitable for
performing time domain reflectometry and/or a first test signal suitable
for performing frequency domain reflectometry.

[0261] In time domain reflectometry, a system response is measured as a
function of time. A test signal suitable for time domain reflectometry
might be, for example, an impulse or narrow transient test signal, e.g.
having a duration of less than 10 ns (which corresponds to an electrical
length of 2 metres).

[0262] In frequency domain reflectometry, a system response is measured as
a function of frequency. A test signal suitable for frequency domain
reflectometry might be, for example, a frequency swept sine wave or
pseudo random noise. Frequency domain information can be converted into a
corresponding time domain response via an inverse Fourier transform, as
would be known to those skilled in the art.

[0263] Preferably, the signal generating unit is configured to generate a
first test signal that is a voltage signal.

[0264] As would be appreciated by a person skilled in the art of signal
processing, a large number of different characteristics of a second test
signal could be analysed to determine whether a second test signal is a
direct signal or a crosstalk signal. Some of these characteristics, and
techniques for analysing these characteristics to distinguish between
direct signals and crosstalk signals are discussed below with reference
to FIGS. 16-21.

[0265] For example, the one or more characteristics of the or each second
test signal analysed by the signal processing unit may include any one or
more of the following characteristics: the amplitude of the second test;
the amplitude of the second test signal as measured at a plurality of
frequencies; an amplitude-frequency characteristic of the second test
signal; an amplitude-distance characteristic of the second test signal;
and an amplitude-time characteristic of the second test signal. However,
this list of characteristics is not thought by the present inventors to
be exhaustive. For example, the one or more characteristics of the or
each second test signal analysed by the signal processing unit may
equally include any one or more of the phase of the second test signal;
or the phase of the second test signal as measured at a plurality of
frequencies.

[0266] For completeness, it is observed that as the velocity of a signal
propagating along a cable is generally constant, time is proportional to
distance and therefore an amplitude-distance characteristic can also be
considered to be an amplitude-time characteristic.

[0267] In some embodiments, the signal generating unit may be configured
to generate a first test signal of a first type and a first test signal
of a second type. The first and second types of first test signal could,
for example, be suitable for performing different types of analysis.
Preferably, the signal processing unit is configured to analyse one or
more characteristics of second test signals of the first type and second
test signals of the second type.

[0268] Preferably, the first type of test signal is a frequency domain
test signal and the second type of test signal is a frequency domain test
signal, with the first type of test signal containing fewer frequency
values than the second type of test signal. Thus, for example, the first
test signal of the first type could be a frequency swept sine wave
containing only eight different frequency values, with the first test
signal of the second type being a frequency swept sine wave containing
one hundred and twenty eight different frequency values.

[0269] If there is a plurality of the second coupling units, the signal
processing unit may be configured to, if more than one of the second
coupling units couples out a respective second test signal of a first
type, analyse one or more characteristics of each respective second test
signal of the first type to establish a shortlist of second coupling
units, the shortlist including the second coupling units which are
identified as having potentially coupled out a direct signal. In this
case, the signal processing unit is preferably further configured to, if
more than one of the shortlisted second coupling units couples out a
respective second test signal of a second type, analyse one or more
characteristics of each respective second test signal of the second type
to determine which, if any, of the respective second test signals of the
second type is a direct signal.

[0270] In this way, the time taken to determine which of a plurality of
second coupling units has coupled out a direct signal can be reduced if,
for example, analysis of the second type of test signal takes longer, but
is more accurate than, the analysis of the first type of test signal.
This might be the case, for example, if the first and second types of
test signal are both frequency domain test signals, with the first type
of test signal containing fewer frequency values than the second type of
test signal, since a frequency domain test signal containing a larger
number of frequency values will generally take longer to analyse but will
generally permit a more accurate determination of whether that test
signal is a direct signal or a crosstalk signal.

[0271] The plurality of cable lines with which the apparatus may be used
could be any type of cable line in which the one or more cables each have
at least two conductors. However, preferably, the plurality of cable
lines each include one or more twisted pair cables, i.e. cables including
a plurality of twisted pairs.

[0272] Preferably, the or each first coupling unit is configured to couple
a respective first test signal generated by the signal generating unit
into a respective first one of the plurality of cable lines such that the
respective first test signal propagates along the respective first cable
line between at least two twisted pairs in the respective first cable
line. Also preferably, the or each second coupling unit is configured to
couple a respective second test signal out from a respective second one
of the plurality of cable lines after it has propagated between at least
two twisted pairs in the respective second cable line.

[0273] Preferably, the or each first coupling unit is configured to couple
a respective first test signal into a respective first one of the
plurality of cable lines by non-contact coupling with the conductors of
the respective first cable line. In this context, non-contact coupling
refers to coupling that does not involve direct electrical (ohmic)
contact with the conductors of the cable line. Likewise, the or each
second coupling unit is preferably configured to couple a respective
second test signal out from a respective second one of the plurality of
cable lines by non-contact coupling with the conductors of the respective
second cable line. However, it is equally possible, and would be within
the capability of a person skilled in the art of signal processing, to
instead use first and second coupling units configured to couple to cable
lines by direct electrical (ohmic) contact with the conductors of the
cable lines.

[0274] Coupling units capable of coupling a test signal generated by a
signal generating unit into (or out from) a twisted pair cable line by
non-contact coupling so that the signal propagates (or after the signal
has propagated) between at least two twisted pairs in the twisted pair
cable line are described below with reference to FIGS. 13-15, and also in
UK patent application number GB0905361.2, U.S. patent application Ser.
No. 11/597,575 and International patent application number
PCT/GB2010/000594, also by the present inventors.

[0275] Accordingly, the or each first coupling unit may include any one or
more of the following features: first and second electrodes arranged to
produce an electric field therebetween to couple a voltage signal (which
may, for example, be a first test signal generated by the signal
generating means) into a twisted pair cable by non-contact coupling with
twisted pairs in the twisted pair cable so that the voltage signal
propagates along the twisted pair cable between at least two of the
twisted pairs; electrical isolation means (e.g. a balun) arranged to
electrically isolate the electrodes from the signal generating unit;
shielding for shielding the electrodes from an external electromagnetic
field; means for converting (e.g. a choke) a single-ended voltage signal
from a signal generating unit into a differential voltage signal to be
coupled to the electrodes; and a housing which may be arranged to be
clipped onto a twisted pair cable.

[0276] Likewise, the or each second coupling unit may include any one or
more of the following features: first and second electrodes arranged to
couple a voltage signal (which may, for example, be a second test signal
resulting from a first test signal coupled into one of the plurality of
cable lines by a first coupling unit) out from a twisted pair cable by
non-contact coupling with at least two of the twisted pairs in the
twisted pair cable between which the voltage signal has propagated;
electrical isolation means (e.g. a balun) arranged to electrically
isolate the electrodes from the signal processing unit; shielding for
shielding the electrodes from an external electromagnetic field; means
for converting (e.g. a choke) a differential voltage signal from the
electrodes into a single-ended voltage signal to be coupled to a signal
processing unit; a housing which may be arranged to be clipped onto a
twisted pair cable.

[0277] The combination of the first and second electrodes with the
electrical isolation means has been found to be particularly preferable
for reducing crosstalk between twisted pair cables, as discussed in UK
patent application number GB0905361.2, U.S. patent application Ser. No.
11/597,575 and International patent application number PCT/GB2010/000594,
also by the present inventors.

[0278] In a second aspect, the present invention provides a signal
processing method according to statement N.

[0279] The method may include any of the features, or method steps
corresponding to the features, described in relation to the first aspect.

[0280] Accordingly, the method may, for example, include coupling, using
each of a plurality of second coupling units, a respective second test
signal out from a respective second one of the plurality of cable lines;
and analysing one or more characteristics of each respective second test
signal to determine, for at least one respective test signal, based on
the one or more analysed characteristics, which, if any, of conditions
(i) and (ii) is true.

[0281] Likewise, the method may, for example, further include: if it is
determined that a second test signal coupled out by a second coupling
unit is a direct signal that has propagated directly from a first
coupling unit to the second coupling unit via a single cable line to
which the first and second coupling units are coupled, identifying an
interconnection between a first port associated with that first coupling
unit and a second port associated with that second coupling unit.

[0282] The invention also includes any combination of the aspects and
preferred features described except where such a combination is clearly
impermissible or expressly avoided.

[0283] Embodiments of our proposals are discussed below, with reference to
the accompanying drawings in which:

[0284] FIGS. 11a and 11b respectively show arrangements which illustrate a
"direct signal" and a "crosstalk signal".

[0286] FIGS. 13a and 13b show a pair of electrodes for coupling a voltage
signal which propagates between twisted pairs into and out from a twisted
pair cable.

[0287] FIG. 14 shows a coupling unit which may be used in the network
interconnection identification apparatus of FIG. 12.

[0288] FIGS. 15a and 15b respectively show a first coupling unit and
circuitry associated with the first coupling unit for coupling a voltage
signal into a twisted pair cable and a second coupling unit and circuitry
associated with the second coupling unit for coupling a voltage signal
out from a twisted pair cable.

[0289] FIG. 16 shows an experimental arrangement for demonstrating the
different characteristics of direct signals and crosstalk signals.

[0290] FIG. 17 shows amplitude-frequency plots for a direct signal and a
corresponding crosstalk signal produced using the apparatus of FIG. 16.

[0291] FIGS. 18a-c are schematic diagrams showing a direct signal and a
crosstalk signal produced using the apparatus of FIG. 16 in the time
domain.

[0292] FIG. 19 shows theoretical amplitude-time plots for the direct
signal and the crosstalk signal described with reference to FIG. 8.

[0293] FIGS. 20a and 20b respectively show amplitude-time plots for a
direct signal and a crosstalk signal produced using the apparatus of FIG.
16.

[0294] FIGS. 21a and 21b respectively show amplitude-distance plots for a
direct signal and a crosstalk signal produced using the apparatus of FIG.
16.

[0295] FIG. 22 shows a typical patch system organised into a server row, a
cross-connect row and a network row.

[0296] FIG. 11a shows an arrangement which illustrates a "direct signal".
The arrangement of FIG. 11a includes a first cable line 110a, a first
("transmitter) coupling unit 120 and a second ("receiver") coupling unit
140. The first coupling unit 120 is configured to couple to a first one
of a plurality of cable lines and to couple a first test signal into that
first cable line such that the first test signal propagates along that
first cable line between at least two conductors in that first cable
line. The second coupling unit 140 is configured to couple to a second
one of a plurality of cable lines and, if a second test signal is present
in that second cable line, to couple the second test signal out from that
second cable line.

[0297] In FIG. 11a, both the first coupling unit 120 and the second
coupling unit 140 are coupled to the same cable line, i.e. the first
cable line 110a. Accordingly, a second test signal coupled out from the
first cable line 110a by the second coupling unit 140 will have
propagated directly from the first coupling unit 120 to the second
coupling unit 140 via a single cable line. A test signal which has
propagated in this way can therefore be referred to as a "direct signal".

[0298] FIG. 11b shows an arrangement which illustrates a "crosstalk
signal". The arrangement of FIG. 11b is the same as that of FIG. 11a,
except that there are additional second and third cables lines 110b,
110c, and the second coupling unit 140 is coupled to a different cable
line from the first coupling unit 120, i.e. to the second cable line 110b
rather than the first cable line 110a. Accordingly, a second test signal
coupled out from the second cable line 110b by the second coupling unit
140 will have propagated indirectly from the first coupling unit 120 to
the second coupling unit 140 via one or more coupling paths between
different cable lines. A test signal which has propagated in this way can
therefore be referred to as a "crosstalk signal". The word "alien" may
optionally be used to describe this crosstalk signal so as to indicate
that the crosstalk occurs between different cable lines, rather than
within a single cable line.

[0299] The one or more coupling paths between the first cable line 110a
and the second cable line 110b are symbolically indicated in FIG. 11b by
arrows. These coupling paths typically include unwanted capacitive and/or
inductive coupling paths and may involve cable lines other than those to
which the first coupling unit 120 and second coupling unit 140 are
respectively coupled, e.g. the third cable line 110c shown in FIG. 11b.

[0300] Note that in FIGS. 11a and 11b, each of the first, second and third
cable lines 110a, 110b, 110c includes a plurality cables (e.g. UTP
cables) whose conductors are directly coupled together by appropriate
connectors 112, e.g. RJ-45 type connectors. However, each of the cable
lines 110a, 110b, 110c could include only one cable. In either case, the
crosstalk signal is different to the direct signal in that it has
propagated between different cable lines via one or more (non-ohmic, e.g.
capacitive or inductive) coupling paths.

[0301] FIG. 12 shows a test signal processing apparatus implemented as a
network interconnection identification apparatus 200 for identifying
interconnections between ports in a network including a plurality of
cable lines.

[0302] FIG. 12 additionally shows a network including plurality of first
cable lines 210a-d connected to a plurality of first ports 213a-d housed
in a first patch panel 215a. The first cable lines 210a-d may, for
example, lead to file servers and switches in a local area network. The
network also includes plurality of second cable lines 210e-h connected to
a plurality of second ports 213e-h housed in a second patch panel 215b.
The first ports 213a-d and second ports 213e-h are interconnected by a
plurality of patch cables 211, although for clarity, only one of the
patch cables 211 is shown in FIG. 12.

[0303] The network interconnection identification apparatus 200 shown in
FIG. 12 has a plurality of first coupling units 220a-d and a signal
generating unit (not shown). The signal generating unit included in the
network identification apparatus 200 may, for example, be as described
below with reference to FIG. 15a.

[0304] Each first coupling unit 220a-d is coupled to a respective first
cable line 210a-d, is associated with a respective port 213a-d in the
first patch panel, and is configured to couple a respective first test
signal generated by the signal generating unit into the respective first
cable line 210a-d such that the respective first test signal propagates
along the respective first cable line 210a-d between at least two
conductors in the respective first cable line 210a-d.

[0305] The apparatus of FIG. 12 also has a plurality of second coupling
units 240a-d and a signal processing unit (not shown). The signal
processing unit included in the network identification apparatus 200 may,
for example, be as described below with reference to FIG. 15b.

[0306] Each second coupling unit 240a-d is coupled to a respective second
cable line 210e-h, is associated with a respective port 213e-h in the
second patch panel 215b, and is configured to, if a respective second
test signal is present in the respective second cable line 210e-h, to
couple the respective second test signal out from the respective second
cable line 210e-h. Typically, a respective second test signal coupled out
from a respective second cable line 210e-h by one of the second coupling
units 240a-d will have resulted from a first test signal coupled into a
respective one of the first cable lines 210a-d by one of the first
coupling units 220a-d.

[0307] The signal processing unit is configured to, if any one or more of
the second coupling units 240a-d couples out a respective second test
signal, analyse one or more characteristics of the or each respective
second test signal to determine, for at least one respective second test
signal, based on the one or more analysed characteristics, which of the
following conditions, if any, is true:

[0308] (i) the respective second test signal is a direct signal that has
propagated directly from a first coupling unit 220a-d to a second
coupling unit 240a-d via a single cable line to which the first and
second coupling units are coupled;

[0309] (ii) the respective second test signal is a crosstalk signal that
has propagated indirectly from a first coupling unit 220a-d to the second
coupling unit 240a-d via one or more coupling paths between different
cable lines to which the first and second coupling units are respectively
coupled.

[0310] Preferably, the signal processing unit is further configured to, if
it determines that a second test signal coupled out by a second coupling
unit 240a-d is a direct signal that has propagated directly from a first
coupling unit 220a-d to the second coupling unit 240a-d via a single
cable line to which the first and second coupling units are coupled,
identify an interconnection between a first port associated with that
first coupling unit 220a-d and a second port associated with that second
coupling unit 240a-d.

[0311] The signal processing unit may additionally or alternatively be
configured to, if it determines that a second test signal coupled out by
a second coupling unit is a crosstalk signal, measure the magnitude of
the crosstalk signal.

[0312] In some embodiments, the signal generating unit may be configured
to generate a first test signal of a first type (e.g. a frequency domain
test signal containing a relatively small number of frequency values,
e.g. eight frequency values) and a first test signal of a second type
(e.g. a frequency domain test signal containing a relatively large number
of frequency values, e.g. one hundred and twenty eight frequency values).
Preferably, the signal processing unit is configured to analyse one or
more characteristics of second test signals of the first type and second
test signals of the second type.

[0313] In some embodiments, the signal processing unit may be configured
to, if more than one of the second coupling units 240a-d couples out a
respective second test signal of the first type, analyse one or more
characteristics of each respective second test signal of the first type
to establish a shortlist of second coupling units 240a-d, the shortlist
including the second coupling units 240a-d which are identified as having
potentially coupled out a direct signal. The signal processing unit is
preferably further configured to, if more than one of the shortlisted
second coupling units 240a-d couples out a respective second test signal
of a second type, analyse one or more characteristics of each respective
second test signal of the second type to determine which, if any, of the
respective second test signals of the second type is a direct signal.

[0314] In FIG. 12, the first cable line 210c is shown as being connected
to the second cable line 210h by the patch cable 211, so the first and
second cable lines 210c, 210h therefore form part of the same (single)
cable line. Accordingly, the first coupling unit 210c and the second
coupling unit 210h as shown in FIG. 12 as being coupled to the same cable
line.

[0315] It should be appreciated that whilst FIG. 12 only shows four of
each of the first cable lines 210a-d, the first ports 213a-d, the first
coupling units 220a-d, the second cable lines 210e-h, the second ports
213e-h, and the second coupling units, a smaller or larger number of each
of these items could easily be used according to network requirements.

[0316] FIGS. 13a and 13b show a pair of electrodes 322a, 322b for coupling
a voltage signal which propagates between twisted pairs into and out from
a twisted pair cable 310. The pair of electrodes 322a, 322b may be used,
for example, in one of the first coupling units 220a-d or one of the
second coupling units 240a-d of the network interconnection
identification apparatus 200 shown in FIG. 12. The electrodes 322a, 322b
shown in FIGS. 13a and 13b are also shown and described in UK patent
application number GB0905361.2, U.S. patent application Ser. No.
11/597,575 and International patent application number PCT/GB2010/000594,
also by the present inventors.

[0317] As shown in FIG. 13a, a first electrode 322a is provided in the
form of a first plate and a second electrode 322b is provided in the form
of a second plate. The electrodes 322a, 322b together form a capacitor.
In this example, the plates forming the first and second electrodes 322a,
322b are approximately 20 mm long and 8 mm wide. The plates may be made
of any suitable material e.g. copper foil.

[0318] The first and second electrodes 322a, 322b are spaced apart to
allow the twisted pair cable 310 to be received therebetween, such that
the electrodes 322a, 322b are located on directly opposite sides of the
twisted pair cable 310. Each of the plates forming the electrodes 322a,
322b has an inwardly curved (i.e. concave) contact surface for contacting
a convex outer surface 314, in this case the outer surface of an
insulating sheath, of the twisted pair cable 310. The curvature of the
contact surfaces of the plates conform to the curvature of the convex
outer surface 314 of the twisted pair cable 310 so that the electrodes
322a, 322b can be held in contact with the convex outer surface 314.

[0319] To couple a voltage signal, e.g. from a signal generating unit,
into the twisted pair cable 310 by non-contact coupling with the twisted
pairs, the voltage signal may be coupled to the electrodes 322a, 322b so
that a corresponding electric field 316 is produced between the
electrodes 322a, 322b. Because the electric field 316 between the first
and second electrodes 322a, 322b is different at twisted pairs 1-2 and
5-6, a voltage is developed between twisted pairs 1-2 and 5-6 which
corresponds to the voltage signal coupled to the electrodes 322a, 322b.
In this way, the voltage signal can be coupled in to the cable 110 such
that it propagates between at least twisted pairs 1-2 and 5-6.

[0320] The electrodes 322a, 322b may additionally or alternatively be used
to couple a voltage signal out from the twisted pair cable 310 by
non-contact coupling with at least two of the twisted pairs between which
the voltage signal has propagated, as shall now be described with
reference to a voltage signal that is propagating between the twisted
pairs 1-2 and 5-6.

[0321] The voltage signal propagating between twisted pairs 1-2 and 5-6 of
the cable 310 will have an electric field 316 between the twisted pairs
1-2 and 5-6 associated therewith. The electric field 316 may cause a
voltage to be developed between the first and second electrodes 322a,
322b which corresponds to the voltage signal between the twisted pairs
1-2 and 5-6. In this way, the voltage signal can be coupled out from the
cable 310 by the electrodes 322a, 322b.

[0322] FIG. 13b shows the pair of electrodes 322a, 322b shown in FIG. 13a,
along with another pair of electrodes 342a, 342b. Electrodes 322a, 322b
may be used as the electrodes of a first coupling unit for coupling a
voltage signal into the twisted cable 310 such that the signal propagates
along the twisted pair cable 310 between at least two twisted pairs in
the twisted pair cable 310. Electrodes 342a, 342b may be used as the
electrodes of a second coupling unit for coupling a voltage signal out
from the twisted pair cable 310 after it has propagated along the twisted
pair cable between at least two of the twisted pairs 310.

[0323] FIG. 13b also shows the twisted pair cable 310 of FIG. 13a in more
detail. As shown in FIG. 13b, not only is each twisted pair 1-2, 3-4,
5-6, 7-8 twisted at a twist rate which is different to that of the other
twisted pairs, but all of the twisted pairs are additionally twisted
around each other. This is typical in a UTP cable.

[0324] Because all the twisted pairs 1-2, 3-4, 5-6, 7-8 of the twisted
pair cable 310 are twisted around each other, the electrodes 342a, 342b
are not necessarily aligned to be adjacent to the same twisted pairs as
the electrodes 322a, 322b of a first coupling unit which coupled a
voltage signal into the twisted pair cable 310. Consequently, the
strength of the signal receivable by the electrodes 342a, 342b varies
between maxima and minima according to their longitudinal position along
the twisted pair cable 310. Varying the circumferential position of the
electrodes 342a, 342b has a similar effect.

[0325] In practice, the inventors have found that a signal of adequate
strength can often be received irrespective of the
longitudinal/circumferential position of the electrodes 342a, 342b.
However, the above-described maxima and minima effect may lead to "null"
locations on the twisted pair cable at which the electrodes 342a, 342b
cannot couple out a voltage signal. Thus, it may be necessary to adjust
the longitudinal/circumferential position of the electrodes 342a, 342b in
order for these electrodes to receive (couple out) a voltage signal
having a desired strength.

[0326] An alternative solution, which avoids the need to adjust the
longitudinal/circumferential position of the electrodes 342a, 342b of the
second coupling unit, is to have two pairs of electrodes, i.e. four
electrodes in total, for coupling a voltage signal to and/or from the
twisted pair cable 310 (not shown). For example, if there are two pairs
of electrodes for coupling the voltage signal out from the twisted pair
cable, an appropriate longitudinal separation between the two pairs of
electrodes could be chosen to ensure that if the first pair of electrodes
was in a "null" position, then the second pair of electrodes would be
near a maximum. A detector and/or a switch could be used to allow the
pair of electrodes receiving the largest voltage signal to be selected,
e.g. by a signal processing unit.

[0327] FIG. 14 shows a coupling unit 420 which may be used in the network
interconnection identification apparatus 200 of FIG. 12, e.g. as a first
or second coupling unit. The coupling unit 420 is capable of coupling a
voltage signal, which may be a test signal, generated by a signal
generating unit into (or out from) a twisted pair cable 410 by
non-contact coupling so that the voltage signal propagates (or after the
signal has propagated) between at least two twisted pairs in the twisted
pair cable 410. The coupling unit shown in FIG. 14 was also shown and
described in UK patent application number GB0905361.2, U.S. patent
application Ser. No. 11/597,575 and International patent application
number PCT/GB2010/000594, also by the present inventors.

[0328] The coupling unit 420 includes a first electrode 422a and a second
electrode 422b. The coupling unit 420 preferably includes a voltage
signal coupling means which may include a first terminal 425a, a second
terminal 425b, an electrical isolating means 424 in the form of a balun,
and a converting means 426 in the form of a choke. The coupling unit 420
preferably includes shielding 429 in the form of an electrostatic screen
which encloses the electrodes 422a, 422b, the electrical isolating means
424 and the converting means 426, and is preferably connected to the
local ground GND, e.g. via the second terminal 425b. A suitable balun for
the electrical isolating means 122 may be Mini-Circuits® type
MCL506T2-T1. A suitable choke for the converting means 124 may be
Mini-Circuits® type MCL750T1-1.

[0329] To couple a voltage signal into a twisted pair cable 410, the first
terminal 425a may be connected to a signal generating unit (not shown).
The second terminal 425b may be connected to a local ground GND for the
signal generating unit.

[0330] A voltage signal generated by the signal generating unit may be a
single-ended voltage signal which is converted into a differential
voltage signal by the converting means 426, e.g. the choke, in the manner
known to those skilled in the art. For example, if the signal generating
unit produced a sinusoidal voltage expressed (in complex phasor notation)
as Vexp(jωt); then the voltages outputted by the converting means
426 may be expressed as Vexp(jωt)/2 and -Vexp(jωt). The
differential voltage signal from the converting means 426 is then coupled
to the electrodes 422a, 422b via the electrical isolating means 424,
which electrically isolates the electrodes 422a, 422b from the signal
generating unit.

[0331] The electrodes 422a, 422b of the coupling unit 420 may be the same
as the electrodes described with reference to FIGS. 13a and 13b, and may
couple the voltage signal into the twisted pair cable 410 in the same
manner.

[0332] As explained in UK patent application number GB0905361.2, U.S.
patent application Ser. No. 11/597,575 and International patent
application number PCT/GB2010/000594, also by the present inventors, the
inventors have found that a voltage signal which propagates along a
twisted pair cable between two of the twisted pairs can propagate
reliably and over useful distances, without significantly altering the
transmission of signals within the individual twisted pairs. In
particular, the inventors have found that coupling a voltage signal to a
twisted pair cable using electrically isolated electrodes can help to
reduce leakage of the voltage signal from the cable, e.g. through
neighbouring twisted pair cables.

[0333] To couple a voltage signal out from the twisted pair cable 410, the
first terminal 425a may be connected to a signal processing unit (not
shown). The second terminal 425b may be connected to a local ground GND
for the signal processing unit.

[0334] The electrodes 422a, 422b of the coupling unit 420 may be the same
as the electrodes described with reference to FIGS. 13a and 13b, and may
couple a voltage signal out from the twisted pair cable 410 in same
manner. The voltage signal coupled out from the twisted pair cable 410
can then be coupled to the signal processing unit via the electrical
isolating means 426 and the converting means 426. The voltage signal
received by the electrodes 422a, 422b may be a differential voltage
signal which may be converted to a single-ended voltage by the converting
means 426, e.g. the choke, in the manner known to those skilled in the
art.

[0335] FIG. 15a shows a first coupling unit 520 and circuitry associated
with the first coupling unit 520 for coupling a voltage signal, e.g. a
first test signal, into a twisted pair cable 510. The first coupling unit
520 may be used in the network interconnection identification apparatus
200 shown in FIG. 12.

[0336] As shown in FIG. 15a, the first coupling unit 520 includes a pair
of electrodes 522a, 522b, an electrical isolating means 524 in the form
of a balun, a converting means 526 in the form of a choke, an amplifier
528, and shielding 529. The electrodes 522a, 522b, the electrical
isolating means 524 and the converting means 526 may be as described
above with reference to FIGS. 13 and 14. The shielding 529 shields the
electrodes 522a, 522b from external electromagnetic fields, e.g. from
other nearby twisted pair cables and nearby coupling units.

[0337] The coupling unit 520 preferably has a housing (not shown) arranged
to be clipped on to the twisted pair cable 510 (e.g. by way of a suitable
channel in the coupling unit or suitable retention lugs) such that the
pair of electrodes 522a, 522b contact directly opposite sides of an outer
surface of the twisted pair cable 510. The housing may include some or
all of the components of the second coupling unit 540.

[0338] The circuitry associated with the first coupling unit 520
preferably includes one or more of a direct signal synthesizer 530, a
field programmable gate array 532, and a processor 536, all of which are
preferably connected as shown in FIG. 15a. The processor 536 may be
connected to, and controlled by, a control unit (not shown) by way of a
serial link 538. The direct signal synthesizer 530, field programmable
gate array 532 and processor 536 may be shared by a plurality of the
first coupling units 520, e.g. in a network interconnection
identification apparatus such as that shown in FIG. 12.

[0339] The circuitry associated with the first coupling unit 520 forms a
signal generating unit configured to generate a voltage signal, e.g. a
first test signal, to be coupled to a twisted pair cable 510 by the
electrodes 522a, 522b of the coupling unit 520. The signal generating
unit may be used, for example, with the network interconnection
identification apparatus 200 shown in FIG. 12.

[0340] In operation, the direct signal synthesizer 530 is preferably
controlled by the field programmable gate array 532 and processor 536 to
generate a voltage signal, e.g. a single-ended voltage signal to be
supplied to the coupling unit 520. Once generated, the single-ended
voltage signal from the direct signal synthesiser 530 is amplified by the
amplifier 528, and is then converted into a differential voltage signal
and coupled to the twisted pair cable 510 by the converting means 524,
the electrical isolating means 522 and the first pair of electrodes 522a,
522b of the coupling unit 520 in the manner described above with
reference to FIGS. 13 and 14, i.e. such that the voltage signal
propagates between at least two of the twisted pairs in the twisted pair
cable 510.

[0341] FIG. 15b shows a second coupling unit 540 and circuitry associated
with the second coupling unit 540 for coupling a voltage signal, e.g. a
second test signal, out from a twisted pair cable 510. The second
coupling unit 540 may be used e.g. in the apparatus shown in FIG. 12.

[0342] As shown in FIG. 15b, the second coupling unit 540 includes a pair
of electrodes 542a, 542b, an electrical isolating means 544 in the form
of a balun, a converting means 546 in the form of a choke, an amplifier
548, and shielding 549. The electrodes 542a, 542b, the electrical
isolating means 524 and the converting means 526 may be as described
above with reference to FIGS. 13 and 14. As with the first coupling unit
shown in FIG. 15a, the shielding 549 shields the electrodes 542a, 542b
from external electromagnetic fields, e.g. from other nearby twisted pair
cables and nearby coupling units.

[0343] As with the first coupling unit shown in FIG. 15a, the second
coupling unit 540 preferably has a housing (not shown) arranged to be
clipped on to the twisted pair cable 510 (e.g. by way of a suitable
channel in the coupling unit or suitable retention lugs) such that the
pair of electrodes 522a, 522b contact directly opposite sides of an outer
surface of the twisted pair cable 510. The housing may include some or
all of the components of the first coupling unit 520.

[0344] The circuitry associated with the second coupling unit 540
preferably includes one or more of a multiplier 549, a direct signal
synthesizer 550, a field programmable gate array 552, a low pass filter
and amplifier 554, an analogue to digital converter 555 and a processor
556, all of which are preferably connected as shown in FIG. 15b. The
processor 556 may be connected to, and controlled by, a control unit (not
shown) by way of a serial link 558. The direct signal synthesizer 550,
the field programmable gate array 552, the low pass filter and amplifier
554, the analogue to digital converter 555, and the processor 556 may be
shared by a plurality of the second coupling units 540, e.g. in a network
interconnection identification apparatus such as that shown in FIG. 12.

[0345] The circuitry associated with the second coupling unit 540,
including the processor 556, forms a signal processing unit configured to
analyse one or more characteristics of a voltage signal, e.g. a second
test signal, coupled out by the second coupling unit 540. The signal
processing unit may be used, for example, with the network
interconnection identification apparatus 200 shown in FIG. 12.

[0346] In operation, when a voltage signal which propagates between
twisted pairs propagates along the twisted pair cable 510 to the second
coupling unit 540, the voltage signal is coupled out of the twisted pair
cable 510 and converted into a single-ended voltage signal by the pair of
electrodes 542a, 542b, the electrical isolating means 544 and the
converting means 546 of the coupling unit 540 in the manner described
above with reference to FIGS. 13 and 14. The single-ended voltage signal
is then amplified by the amplifier 548, demodulated by the multiplier 549
and the low pass filter and amplifier 554 and is then passed to the
analogue to digital converter 550 where it is converted into a digital
signal. A final stage of demodulation is performed by the field
programmable gate array 552 and the digital signal is then passed to the
processor 556.

[0347] A plurality of the first coupling units 520 shown in FIG. 15a may
be used as first coupling units in the network interconnection
identification apparatus 200 shown FIG. 12, with the associated circuitry
shown in FIG. 15a being used as the signal generating unit for generating
a first test signal. Similarly, a plurality of the second coupling units
540 shown in FIG. 15b may be used as second coupling units in the network
interconnection identification apparatus 200 shown in FIG. 12, with the
associated circuitry shown in FIG. 15b being used as the signal
processing unit for determining, for at least one respective test signal,
which of conditions (i) and (ii), if any, is true. This determination
could, for example, be made by the processor 556.

[0348] As would be appreciated by a person skilled in the art of signal
processing, a large number of different characteristics of a second test
signal could be analysed by the signal processing unit to determine
whether a second test signal is a direct signal or a crosstalk signal.
Some of these characteristics, and techniques for analysing these
characteristics to distinguish between direct signals and crosstalk
signals will now be discussed, with reference to FIGS. 16-21.

[0349] FIG. 16 shows an experimental arrangement 600 for demonstrating the
different characteristics of direct signals and crosstalk signals.

[0350] The experimental arrangement 600 shown in FIG. 16 has first and
second cables 610a, 610b, which are separate and unterminated lengths of
category 5 UTP cable that have been taped closely together by tape 616.

[0351] A first coupling unit 620, which has features corresponding to the
first coupling unit 520 shown in FIG. 15a, is coupled to the first cable
610a to allow the first coupling unit 620 to couple a first test signal
into the first cable 610a. Two second coupling units 640a, 640b, each
having features corresponding to the second coupling unit 540 shown in
FIG. 15b, are each coupled to a respective one of the first and second
cables 610a, 610b at an opposite end from the first coupling unit 620.
The second coupling unit 640a is attached to the first cable 610a, i.e.
the same cable as the first coupling unit 620, and therefore will couple
out a second test signal that is a direct signal. The other of the second
coupling units 640b is attached to the second cable 610b, i.e. a
different cable from the cable to which the first coupling unit 620 is
coupled, and will therefore couple out a second test signal that is a
crosstalk signal.

[0352] FIG. 17 shows amplitude-frequency plots for a direct signal 760 and
a crosstalk signal 780 produced using the apparatus 600 of FIG. 16. To
produce the plot shown in FIG. 17, category 5 UTP cables of length 2
metres were used as the first and second cables 600a, 600b. The first
test signal coupled into the first cable 610a was a wideband frequency
sweep from 956 kHz to 300 MHz containing approximately 1000 different
frequencies. The phase and magnitude of the second test signal coupled
out by the second coupling units 640a, 640b were recorded. The recorded
phase and magnitude data was used directly to produce the
amplitude-frequency plots of FIG. 17.

[0353] As shown in FIG. 17, the average (e.g. root mean square) amplitude
(energy) of the direct signal 760 generally higher than that of the
crosstalk signal 780. Therefore, the amplitude of a second test signal
coupled out by a second coupling unit at a selected frequency is
indicative of whether that second test signal is a direct signal or a
crosstalk signal.

[0354] Accordingly, the one or more characteristics of a second test
signal analysed by a signal processing unit to determine whether that
second test signal is a direct signal or a crosstalk signal may include
the amplitude of the second test signal.

[0355] As would be appreciated by a person skilled in the art of signal
processing, there are a large number of possible techniques for analysing
the amplitude of a second test signal to determine whether that second
test signal is a direct signal or a crosstalk signal.

[0356] A potential issue with analysing the amplitude of a test signal to
distinguish between direct and crosstalk signals is illustrated by FIG.
17. Here, the respective amplitudes of the direct signal 760 and the
crosstalk signal 790 (particularly the crosstalk signal 780) are strongly
dependent on frequency. Thus, whilst the amplitude of the direct signal
760 is larger than the amplitude of the crosstalk signal 780 for most
frequencies, there are certain frequencies at which the amplitude of the
crosstalk signal 780 is larger than the amplitude of the direct signal
760 (see the circled portions of FIG. 17). For a given cable, these
certain frequencies typically correspond to values of the resonant
frequencies of the cable, which are determined by the length and
termination conditions of the cable. The amplitude of the crosstalk
signal may therefore be higher where the resonances in the first and
second cables 610a, 610b overlap.

[0357] To address this issue, in a presently preferred technique, the one
or more characteristics of a second test signal analysed by a signal
processing unit to determine whether that second test signal is a direct
signal or a crosstalk signal include the amplitude of the second test
signal as measured at a plurality of frequencies.

[0358] For example, the amplitude of the second test signal could be
measured at nine different frequencies 790, as shown in FIG. 17.
Preferably, the frequencies 790 are non-integer multiples of each other,
in order to avoid harmonics. Preferably, the different frequencies 790
are in the range 30 to 150 MHz. The amplitude of the second test signal
measured at each frequency could, for example, be combined (e.g. using a
weighted sum) to create a parameter which characterises the overall
amplitude of the signal over a frequency range. If the parameter exceeds
an upper threshold, then the second test signal could be determined to be
a direct signal. If the parameter is below a lower threshold, then the
second test signal could be determined to be a crosstalk signal. If the
parameter was in between the upper and lower thresholds, then the second
coupling unit that coupled out the second test signal could be
shortlisted as having potentially coupled out a direct signal. Suitable
upper and/or lower thresholds could be determined empirically.

[0359] As illustrated by FIG. 17, the amplitude-frequency plot for the
direct signal 760 has a different shape to the amplitude-frequency plot
for the cross-talk signal 780. In particular, the amplitude-frequency
plot for the crosstalk signal 780 has sharper resonances, which reflect,
for example, cable length and the coupling paths between the first and
second cables 610a, 610b.

[0360] Accordingly, the one or more characteristics of a second test
signal analysed by a signal processing unit to determine whether that
second test signal is a direct signal or a crosstalk signal may include
an amplitude-frequency characteristic of the test signal, e.g. a
parameter which reflects the shape of an amplitude-frequency plot for the
test signal.

[0361] FIGS. 18a-c are schematic diagrams showing a direct signal 860 and
a crosstalk signal 880 produced using the apparatus 600 of FIG. 16 in the
time domain. To produce the signals depicted in FIGS. 18a-c, a transient
first test signal including one cycle of a sine wave is assumed to have
been coupled into the first cable 610a by the first coupling unit 620.
The transient first test signal could be generated, for example, using a
frequency sweep and Fourier analysis techniques, which are known in the
art.

[0362] FIGS. 18a-c show a plurality of coupling paths 619 between the
first cable 610a and the second cable 610b, via which energy coupled into
the first cable 610a may propagate into the second cable 610b. In FIG.
18, the coupling paths 619 are depicted as capacitive coupling paths.

[0363] As shown in FIG. 18b, the direct signal 860 propagates along the
first cable 610a in both directions and the passage of the direct signal
along the first cable 610a is recorded at the second coupling unit 640a.
If the cable is long (such as tens of meters) or is terminated with
resistors that are impedance matched to the characteristic impedance of
the cable, and in addition, if the cable has no discontinuities such as
connectors, then the direct signal 860 will propagate without significant
reflections, and will simply attenuate with distance, as shown in FIG.
18b.

[0364] As shown in FIG. 18c, the crosstalk signal 880 is coupled into the
second cable 610b in a distributed manner via the coupling paths 619
along the length thereof. Accordingly, the crosstalk signal 880 received
by the second coupling unit 640b is dispersed over a longer period of
time, as shown in FIG. 18c. The crosstalk signal will be stronger if the
first and second cables 610a, 610b have a similar construction.

[0365] FIG. 19 shows theoretical amplitude-time plots for the direct
signal 860 and the crosstalk signal 880 described with reference to FIG.
18.

[0366] As shown in the upper plot of FIG. 19, the direct signal 860 tends
to attenuate with time. This is because all the energy from the transient
first test signal is coupled into the first cable 610a cable over a
relatively short interval of time. The direct signal 860 therefore
propagates along the first cable 610a in both directions. Reflections are
caused by changes in impedance along the cable, but overall the magnitude
of the signal decays in time as the energy coupled by the transmitter
dissipates in the cable due to resistive, capacitive and inductive
losses.

[0367] As shown in the lower plot of FIG. 19, the crosstalk signal 880
behaves differently to the direct signal 860. Here, energy from the
transient first test signal is coupled into the second cable 610b over a
period of time and the coupling is distributed over the length of the
second cable 610b. Consequently, the crosstalk signal 880 builds up over
an initial period as the transient test signal propagates forward and
backward along the second cable 610b.

[0368] After a period of time both the direct signal 860 and the crosstalk
signal 880 decay to zero as the energy dissipates due to resistive,
capacitive and inductive losses in the first and second cables 610a,
610b.

[0369] FIGS. 20a and 20b respectively show amplitude-time plots for a
direct signal 1060 and a crosstalk signal 1080 produced using the
apparatus 600 of FIG. 16. The amplitude-time plots of FIGS. 20a and 20b
were produced by using a Fourier transform to transform the phase and
magnitude data recorded to produce the plots of FIG. 17, for which
category 5 UTP cables of length 2 metres were used.

[0370] FIG. 20a clearly shows the amplitude of the direct signal 1060
decaying over time. FIG. 20b shows that, in contrast to the direct signal
1060, the amplitude of the crosstalk signal 1080 initially builds up,
this initial build up being followed by a gradual decay over the
remaining period.

[0371] As can be seen from FIGS. 18-20, the amplitude-time characteristics
for a direct signal are different to the amplitude-time characteristics
for a crosstalk signal. In particular, a crosstalk signal is dispersed
over a longer period of time than a direct signal, and a crosstalk signal
builds-up gradually and then decays rather than simply decaying in the
manner of a direct signal.

[0372] Accordingly, the one or more characteristics of a second test
signal analysed by a signal processing unit to determine whether that
second test signal is a direct signal or a crosstalk signal may include
an amplitude-time characteristic of the test signal.

[0373] As would be appreciated by a person skilled in the art of signal
processing, there are a large number of possible techniques for analysing
one or more amplitude-time characteristics of a second test signal to
determine whether that second test signal is a direct signal or a
crosstalk signal.

[0374] A presently preferred technique involves calculating the root mean
square of the amplitude of the second test signal for each of a plurality
of time intervals. In other words, the amplitude-time characteristic of
the second test signal may include the root mean square of the amplitude
of the second test signal as calculated for each of a plurality of time
intervals.

[0375] For the data recorded in FIGS. 20a and 20b, the root mean square of
the amplitude of the second test signals was calculated for eleven time
intervals of duration 50 ns, starting from 0 ns as marked in FIGS. 20a
and 20b (i.e. from 0 ns to 50, 50 ns to 100 ns and so on with the last
time interval being 500 ns to 550 ns). A direct signal will have the
largest root mean square value during the first 50 ns time interval than
in subsequent time intervals. The crosstalk signal on the other hand will
have a different profile, with the largest root mean square value not
being during the first 50 ns time interval.

[0376] FIGS. 21a and 21b respectively show amplitude-time plots for a
direct signal 1160 and a crosstalk signal 1180 produced using the
apparatus 600 of FIG. 16. To produce the plot shown in FIG. 21, category
5 UTP cables of length 90 metres were used. The first test signal coupled
into the first cable 610a was a transient first test signal including
several cycles of a sine wave, and was produced using a frequency sweep
and Fourier analysis techniques, which are known in the art.

[0377] As shown in FIG. 21, the direct signal 1160 has a large initial
amplitude. In addition a reflection 1190 from an end of the first cable
610a is also visible. The shape of the direct signal 1160 is consistent
with the transient first test signal. The crosstalk signal 1180 on the
other hand has lower overall amplitude, and does not display a shape
consistent with a signal that has propagated along a single cable line.

[0378] As can be seen from FIG. 21, the amplitude-time characteristics for
a direct signal are different to the amplitude-time characteristics for a
crosstalk signal. In particular, the crosstalk signal 1180 is dispersed
over a longer period of time than the direct signal.

[0379] As already noted above, the one or more characteristics of a second
test signal analysed by a signal processing unit to determine whether
that second test signal is a direct signal or a crosstalk signal may
include an amplitude-time characteristic of the second test signal.

[0380] Another possible technique for analysing one or more amplitude-time
characteristics of a second test signal to determine whether that second
test signal is a direct signal or a crosstalk signal involves
cross-correlating each of a plurality of second test signals coupled out
by second coupling units with a reference signal known to be a direct
signal. Cross-correlating a direct signal would produce a peak in the
cross-correlated signal. The position of the peak on the time axis would
correspond to the time of propagation of the signal from the first
coupling unit to the second coupling unit. As the speed of propagation
for the cable is constant, this would correspond to the electrical length
of the cable between the two coupling units. Cross-correlating a
crosstalk signal would produce a cross-correlated signal having values
close to zero. A threshold, e.g. determined empirically, could be applied
to the cross-correlated signal to determine whether each second test
signal coupled out by the second coupling units is a direct signal or a
crosstalk signal.

[0381] Where the length of the cable lines 610a, 610b is short compared to
the length of the transient test signal coupled into the first cable line
610a by the first coupling unit 620, for example just several meters, the
multiple reflections from any unterminated ends of the cable and from
discontinuities may start to overlap. In this case, the time domain
response becomes more complicated than that shown in FIG. 21 (as
illustrated e.g. by FIGS. 20a and 20b). Nevertheless, even in these
cases, it has been found that a direct signal can still be clearly
differentiated from a crosstalk signal.

[0382] When used in this specification and statements, the terms
"comprises" and "comprising" and variations thereof mean that the
specified features, steps or integers are included. The terms are not to
be interpreted to exclude the presence of other features, steps or
integers.

[0383] The features disclosed in the foregoing description, or in the
following statements, or in the accompanying drawings, expressed in their
specific forms or in terms of a means for performing the disclosed
function, or a method or process for obtaining the disclosed results, as
appropriate, may, separately, or in any combination of such features, be
utilised for realising the invention in diverse forms thereof.

[0384] While the invention has been described in conjunction with the
exemplary embodiments described above, many equivalent modifications and
variations will be apparent to those skilled in the art when given this
disclosure, without departing from the broad concepts disclosed. It is
therefore intended that the scope of the patent granted hereon be limited
only by the appended statements, as interpreted with reference to the
description and drawings, and not by limitation of the embodiments
described herein.

STATEMENTS

[0385] A. A signal processing apparatus for use with a plurality of cable
lines, the signal processing apparatus having:

[0386] a signal generating unit configured to generate a first test
signal;

[0387] a first coupling unit configured to couple to a first one of the
plurality of cable lines and to couple a first test signal generated by
the signal generating unit into the first cable line such that the first
test signal propagates along the first cable line between at least two
conductors in the first cable line;

[0388] a second coupling unit configured to couple to a second one of the
plurality of cable lines and, if a second test signal is present in the
second cable line, to couple the second test signal out from the second
cable line; and

[0389] a signal processing unit configured to, if the second coupling unit
couples a second test signal out from a second one of the plurality of
cable lines, analyse one or more characteristics of the second test
signal to determine, based on the one or more analysed characteristics,
which of the following conditions, if any, is true:

[0390] (i) the second test signal is a direct signal that has propagated
directly from the first coupling unit to the second coupling unit via a
single cable line to which the first and second coupling units are
coupled;

[0391] (ii) the second test signal is a crosstalk signal that has
propagated indirectly from the first coupling unit to the second coupling
unit via one or more coupling paths between different cable lines to
which the first and second coupling units are respectively coupled.

B. A signal processing apparatus according to statement A wherein:

[0392] the apparatus has a plurality of first coupling units, each first
coupling unit being configured to couple to a respective first one of the
plurality of cable lines and to couple a respective first test signal
generated by the signal generating unit into the respective first cable
line such that the respective first test signal propagates along the
respective first cable line between at least two conductors in the
respective first cable line;

[0393] the apparatus has a plurality of second coupling units, each second
coupling unit being configured to couple to a respective second one of
the plurality of cable lines and, if a respective second test signal is
present in the respective second cable line, to couple the respective
second test signal out from the respective second cable line;

[0394] the signal processing unit is configured to, if any one or more of
the second coupling units couples out a respective second test signal,
analyse one or more characteristics of the or each respective second test
signal to determine, for at least one respective second test signal,
based on the one or more analysed characteristics, which of the following
conditions, if any, is true:

[0395] (i) the respective second test signal is a direct signal that has
propagated directly from a first coupling unit to a second coupling unit
via a single cable line to which the first and second coupling units are
coupled;

[0396] (ii) the respective second test signal is a crosstalk signal that
has propagated indirectly from a first coupling unit to the second
coupling unit via one or more coupling paths between different cable
lines to which the first and second coupling units are respectively
coupled.

C. A test signal processing apparatus according to statement A or B
wherein:

[0397] the signal processing unit is configured to, if it determines that
a second test signal coupled out by a second coupling unit is a direct
signal that has propagated directly from a first coupling unit to the
second coupling unit via a single cable line to which the first and
second coupling units are coupled, identify an interconnection between a
first port associated with that first coupling unit and a second port
associated with that second coupling unit.

D. A test signal processing apparatus according to any one of the
previous statements wherein the signal processing unit is configured to,
if it determines that a second test signal coupled out by a second
coupling unit is a crosstalk signal, measure the magnitude of the
crosstalk signal. E. A test signal processing apparatus according to any
one of the previous statements wherein the signal generating unit is
configured to generate a first test signal suitable for performing time
domain reflectometry and/or a first test signal suitable for performing
frequency domain reflectometry. F. A test signal processing apparatus
according to any one of the previous statements wherein the one or more
characteristics of the or each second test signal analysed by the signal
processing unit may include any one or more of the following
characteristics:

[0398] the amplitude of the second test signal;

[0399] the amplitude of the second test signal as measured at a plurality
of frequencies;

[0400] the phase of the second test signal;

[0401] the phase of the second test signal as measured at a plurality of
frequencies;

[0402] an amplitude-frequency characteristic of the second test signal;

[0403] an amplitude-distance characteristic of the second test signal; and

[0404] an amplitude-time characteristic of the second test signal.

G. A test signal processing apparatus according to any one of the
previous statements wherein:

[0405] the signal generating unit is configured to generate a first test
signal of a first type and a first test signal of a second type.

H. A test signal processing apparatus according to any one of the
previous statements wherein:

[0406] there is a plurality of the second coupling units;

[0407] the signal processing unit is configured to, if more than one of
the second coupling units couples out a respective second test signal of
a first type, analyse one or more characteristics of each respective
second test signal of the first type to establish a shortlist of second
coupling units, the shortlist including the second coupling units which
are identified as having potentially coupled out a direct signal; and

[0408] the signal processing unit is further configured to, if more than
one of the shortlisted second coupling units couples out a respective
second test signal of a second type, analyse one or more characteristics
of each respective second test signal of the second type to determine
which, if any, of the respective second test signals of the second type
is a direct signal.

I. A test signal processing apparatus according to any one of the
previous statements wherein the plurality of cable lines each include one
or more twisted pair cables. J. A test signal processing apparatus
according to statement 9 wherein:

[0409] the or each first coupling unit is configured to couple a
respective first test signal generated by the signal generating unit into
a respective first one of the plurality of cable lines such that the
respective first test signal propagates along the respective first cable
line between at least two twisted pairs in the respective first cable
line; and

[0410] the or each second coupling unit is configured to couple a
respective second test signal out from a respective second one of the
plurality of cable lines after it has propagated between at least two
twisted pairs in the respective second cable line.

K. A test signal processing apparatus according to any one of the
previous statements wherein:

[0411] the or each first coupling unit is configured to couple a
respective first test signal into a respective first one of the plurality
of cable lines by non-contact coupling with the conductors of the
respective first cable line; and/or

[0412] the or each second coupling unit is preferably configured to couple
a respective second test signal out from a respective second one of the
plurality of cable lines by non-contact coupling with the conductors of
the respective second cable line.

L. A test signal processing apparatus according to any one of the
previous statements wherein the or each first coupling unit includes:

[0413] first and second electrodes arranged to produce an electric field
therebetween to couple a voltage signal into a twisted pair cable by
non-contact coupling with twisted pairs in the twisted pair cable so that
the voltage signal propagates along the twisted pair cable between at
least two of the twisted pairs; and

M. A test signal processing apparatus according to any one of the
previous statements wherein the or each second coupling unit includes:

[0415] first and second electrodes arranged to couple a voltage signal out
from a twisted pair cable by non-contact coupling with at least two of
the twisted pairs in the twisted pair cable between which the voltage
signal has propagated; and

[0418] coupling, using a first coupling unit, the first test signal into a
first one of a plurality of cable lines such that the first test signal
propagates along the first cable line between at least two conductors in
the first cable line;

[0419] coupling, using a second coupling unit, a second test signal out
from the second cable line; and

[0420] analysing one or more characteristics of the second test signal to
determine, based on the one or more analysed characteristics, which of
the following conditions, if any, is true:

[0421] (i) the second test signal is a direct signal that has propagated
directly from the first coupling unit to the second coupling unit via a
single cable line to which the first and second coupling units are
coupled;

[0422] (ii) the second test signal is a crosstalk signal that has
propagated indirectly from the first coupling unit to the second coupling
unit via one or more coupling paths between different cable lines to
which the first and second coupling units are respectively coupled.

O. A signal processing method according to statement N, wherein the
method further includes if it is determined that a second test signal
coupled out by a second coupling unit is a direct signal that has
propagated directly from a first coupling unit to the second coupling
unit via a single cable line to which the first and second coupling units
are coupled, identifying an interconnection between a first port
associated with that first coupling unit and a second port associated
with that second coupling unit. P. A signal processing apparatus
substantially as any one embodiment herein described with reference to
and as shown in the accompanying drawings. Q. A signal processing method
substantially as any one embodiment herein described with reference to
and as shown in the accompanying drawings.